Aquaria features the Rainbow Mushroom...which doesn't do anything on its own, but mixed into Hot Soup it makes Rainbow Soup, whose effect is listed as "trippy". What this gets you is the same Interface Screw animation as a faceful of squid ink, but in rainbow colors. For about thirty seconds, anyway; after that the colors darken almost to black as Naija experiences the crash that almost never comes with this trope, letting out pained gasps at an alarming rate until the soup wears off after another thirty seconds or so.
Arknights: During the event "Gavial The Great Chief Returns" Caster operator Ceobe ate some mushrooms in the forest, which turned out to be poisonous and caused her to hallucinate the events in the first season of Integrated Strategies "Ceobe's Fungimist".
Assassin's Creed: Valhalla has these in the Fly Agaric type of Mysteries where Eivor can find a patch of red-capped mushrooms where they end up going on one hell of a trip. They have to read the note left behind to find their way back to reality while also at the same time opening up their mind.
The sidequest "Have You Seen This Man" has them join Petra, a hunter in Ravensthorpe as she looks for her brother Wallace. They track him down to his camp and get a whiff of a noxious soup that leads them on a trip involving a mystical white elk, the Jotnar, Petra trying to ask the squirrels if they saw him, but they only speak rabbit. They end up making a full circuit back home and Wallace is behind them, having had the same bad trip from the mushroom soup.
While the Kid in Bastion doesn't really take anything, wandering around in Jawson Bog (which the Kid is warned about before hand that "That place'll eat your mind") eventually causes him to start having some rather disturbing hallucinations (including the narrator Rucks sounding more unhinged and hostile), hinting at the Kid suffering from Survivor's Guilt.
In Batman: Arkham Asylum: Batman wanders into three areas where Scarecrow is present and comes under effect of his fear toxin which starts changing the landscape before thrusting Batman in a nightmare world where he has to avoid the gaze of a giant Scarecrow and reach bat-signals to drive him off. The first two times Batman snaps out of it, he's in different areas meaning he somehow made his way to them through the hallucinations. The third showing it happens as a Mind Screw to the players by having the game lock up and suddenly restarting to the intro sequence.
Batman: Arkham City: When Batman takes the League of Assassin's trials by drinking some of the Lazarus Pit, the liquid's effect has him suddenly in a desert like landscape where he has to follow Ra's al Ghul and fight several clones of him before he can pass. The battle against Ra's also takes place in the same landscape for some reason. Also while not drug related, the side mission with the Mad Hatter has undertones of this via his mind-control mask.
Batman: Arkham Origins: Again the Mad Hatter side mission, which is longer this time has you traversing a rather whack out version of Wonderland while trying to track him due to some hypnotic device.
Batman: Arkham Knight, as Scarecrow is the main Big Bad of the story, this pops up a few times such as in the intro sequence where he tests a new fear toxin on a diner causing everyone to hallucinate seeing zombies attacking them. Batman gets sprayed with the toxin a few times, causing him to see Joker for the rest of the game as well as what he thinks is Barbara/Oracle's death in the middle of it as well as a few mind screw sequences such as battling dozens of Jokers where he's eventually forced to confront breaking his one rule: killing someone.
Makoto's gag reel in BlazBlue: Chronophantasma essentially amounts to this when she receives candy from Kokonoe, which she shares with Taokaka and Valkenhayn. Allegedly, it's supposed to awaken the inner beast, but somewhere along the line Taokaka pulls Makoto's tail off... and then the severed tail somehow comes to life! Can you make shit like this up sober?
Blood had delirium shrooms, which showed up in the beta versions, but were never used in the final game (though some user-made level packs such as Bloody Pulp Fiction use them). They caused the camera to wobble and sound to distort for a few seconds, rendering the game almost unplayable.
Bug Too! has the final stages of the game, Cicada Night Fever. The entire level is one hell of an acid trip — the platforms are unnaturally colorful, the background contains Dali's clocks, you fight toads (from the first game) and floating Cheshire Cats, and the Final Boss? Three of that smoking caterpillar from Alice in Wonderland... while deadly popcorn rains down from the sky.
A lore room in Dead Cells features a mycologist. The Beheaded finds a cash register in his cell, and deduces that he used his skills to supply the whole prison with hallucinogens.
In Deus Ex, you can make the main character smoke cigarettes, drink alcohol and even do drugs. The cigarettes make him cough and lose health. The booze actually increases health a little, but makes vision worse. The drug (called "Zyme") has no effect on health, but screws up your vision for a long time.
In Donkey Kong Country Returns, DK and Diddy find a magic floating golden banana in the final level. After digging in, they find themselves in a mysterious land in the sky full of floating fruit platforms and koalas that are also half helicopter. One might argue that this wasn't a hallucination and they were actually transported to a land where giant cherries are actually proximity bombs. One might also be a little naive.
In Dragon Age: Inquisition, Blackwall, providing that you completed his character quest, mentions a previous assignment where he and his team lost all of their food to a flash flood. All that left them with were the berries that the newest member of the group had found. For the next two days, Blackwall thought he was surrounded by a ring of nugs that were singing sea shanties.
A woman in Summers allows Ness to eat "Magic Cake", which allows Ness to have a vision of Poo.
Being hit by a walking mushroom's blast can make a mushroom grow from your head, which randomly changes the direction keys. Also causes confusion in battle until removed by a guy... who eats it.
To say nothing of the coffee a Mr. Saturn offers. Though really, speaking to your dad inside a Kaleidoscope is nowhere near as bizarre as... everything else in the entire game.
What about Moonside? Or are we blaming that on the Mani Mani statue?
When the party is forced to eat some strange mushrooms found in the jungle — in this case, it serves as a rather spiteful Journey to the Center of the Mind, as the hallucinogen preys on 'guilts and fears' (the party's dog is the only one not taken in). The events were apparently supposed to be even more horrible, but the creator decided to tone it down.
Claus: Everyone's waiting for you. Everyone's waiting to throw rocks at you, spit on you, and make your life hell. Who's "everyone"...? Everyone you love.
Thankfully for poor Lucas, his next high — the return of the Saturns' coffee from the EarthBound (1994) — is much less horrific.
The Game Mod Claus' Journey allows you to have Claus as the protagonist instead of Lucas, and the dialogue from the hallucinations during the events of Tanetane Island is a more jarring from his perspective.
Lucas: "Let's switch places. Let's switch places. Claus. Claus. Let's switch places. You can be the dead one! YOU CAN BE THE DEAD ONE!"
Flint: "You're a horrible son, Claus. You let your Mother die, you got your brother killed. And now you've left your dear old Dad to continue to go crazy from grief all alone. It's no wonder why I neglect you and keep searching for my better son, you Bastard."
Fallout 3's expansion, "Point Lookout", features an encounter with a psychoactive fruit which explodes in the player's face... followed by having a lobotomy while the player character is hallucinating.
To say nothing about Vault 106 in the base game, whose experiment was to pump hallucinatory drugs into the air system and observe how the occupants reacted; said reaction was to go insane and murder everyone else inside the vault. If the Lone Wanderer goes inside for a length of time, he starts to experience the effects firsthand, which manifest as unusual messages to himself on the computers and multiple illusions of his father and childhood friend.
In the "Rite of Passage" quest from the Fallout: New Vegas DLC Honest Hearts, the Courier trips out on Datura tea, and has to fight a flaming yao guai ghost, which is just as deadly as its regular brethren.
Far Cry 3 has multiple interactive instances of this, induced by everything from hallucinogenic mushrooms, mystical potions, or just good old fashioned drugs. The moment that really stands out is the mission where Jason's sent to torch a bunch of marijuana plantations with a flamethrower. He starts getting a contact high from all the smoke and quite clearly having the time of his life; all the while, this music's blaring in the background.
Continued in Far Cry 4, which has a mission where you get high on the fumes inside an opium factory, an entire questline based around a pair of stoners testing their new formulas on you, and a level where you are thrown into prison and drugged. Then you have to flee from hallucinatory demons.
Far Cry 5 continues the tradition via a mind-control drug used by the cult. Faith Seed in particular has the ability to speak to in your mind solely through hallucinations.
The intro to Frederic: Resurrection of Music's Caribbean stage has Rob blowing a cloud of smoke that makes the beach scenery more colorful. In the end, it's implied that everything that happened there was just Chopin tripping off second-hand marijuana smoke.
In Grand Theft Auto III and Vice City, when you take the adrenaline pills everything becomes very slow and everyone speaks in low, distorted voices. Also, the player becomes super strong and fast. One mission in Vice City starts after you encounter a side character's boomshine. You have to drive him to the hospital while very, very drunk. Something similar happens in Grand Theft Auto: San Andreas, where you end up driving a van under the influence of weed after helping the van's owner torch an entire field of weed with a flamethrower. It happens yet again in Grand Theft Auto: Vice City Stories, when during one mission the protagonist is knocked unconscious with his face in a pile of cocaine, and has to complete the rest of the mission high after he wakes up.
In Grand Theft Auto IV, the player character can also get drunk, with realistic driving impairment effects.
Grand Theft Auto V also features several different sequences fueled by psychedelic drugs, including a hallucination of being abducted by aliens, then being ejected from the UFO and free-falling over Los Santos half-naked, and mowing down wave after wave of evil clowns (or xenomorphs, depending on whether you're doing Trevor or Michael's part of that quest). There are also hidden peyote cacti that when ingested, causes the character to trip as an animal for a certain period of time, accompanied with a narrative from the character.
Grand Theft Auto Online in the "Los Santos Drug Wars" DLC, the player gets to meet The Fooliganz, who aim to corner the LSD trade in Los Santos. After helping them set up their new headquarters, they treat the player character(s) to a beer, which soon causes them to start seeing colors and the people around them change shape, and once the trip fully kicks in, the player(s) get to follow the leader Dax on a BMX as the hallucinations get more and more intense, until waking up in just underwear. Later, when helping the Fooliganz save their Clandestine Chemist Labrat from Dr. Friedlander, the player(s) are hit with a hallucigenic gas and have to have a trippy gun fight in the yard of a rehab centre, including shooting clones of the player character. There is also a side mission where the player has to destroy Epsilonist weed farms, and the chemicals cause them to hallucinate endless waves of evil clows attacking them until the timer runs out.
When you help Lil' Smoke in Hell Pie, it takes you an island where he does his drug-manufacturing. Since he deals in hallucinogenic drugs, the whole thing looks like it takes place in the clouds with rainbow bridges, Nugget's dialogue implying just how high he is.
In (the already trippy) Hotline Miami 2: Wrong Number, the Son gets one of these after he has a bit too much of his own product. In it, he slaughters both the Fans — in the form of hallucinations of animals of the masks they wear — and his own henchmen before walking off the edge of a building, seeing a rainbow bridge to Heaven.
In the first game, in an alternate reality the Joker steals Scarecrow's fear toxin and causes Superman to mistake a pregnant Lois Lane for Doomsday. The ensuing fight obviously ends with the gruesome deaths of Lois and their baby. When Superman realizes what he's done, he Goes Mad from the Revelation and becomes the Big Bad of the series. Scarecrow himself only appears in a cameo though. In the Arkham stage, if the opponent is knocked into just the right spot, he'll run out, gas them, and the character briefly goes into Scarecrow's nightmare sequence from Batman: Arkham Asylum before getting knocked into another part of the stage.
In Injustice 2, Scarecrow is a playable character and he makes this trope into his entire fighting style. He has no powers or weapons of his own, and before the match we see he's wearing a normal suit and burlap hood as he turns on his fear gas. His monstrous appearance, supernatural abilities, and even his chain and sickle are all hallucinations his opponent is experiencing. Even in his prefight banter, he tries to get under his opponent's skin with personal details about them that he couldn't possibly know, like Supergirl's past on Krypton. That's when you realize Scarecrow doesn't actually know these things; it's the fear gas messing with the opponent's mind.
Jazz Jackrabbit 2 has an afro-wearing caterpillar enemy, resting on a toadstool (inspired by Alice in Wonderland) who blows out ring-shaped puffs of smoke. When the player hits one of these smokerings, the entire stage's colours start to cycle around psychedelically for a few moments, and the player's movement becomes distorted for a moment (Left is Right, etcetera).
Kingdom Come: Deliverance has Henry meet a group of women who bought hallucinogenic ointment from a witch in the hopes of seeing their loved ones again. Should Henry be spotted after they've applied it, they mistake him for Lucifer come to grant them their wish, only to smear the ointment on him as well and Hilarity Ensues.
Knytt Stories has Don't Eat the Mushroom, played by ProtonJonhere. If you eat the mushroom, you go through a series of trippy scenes from the Burger King over a fiery background to Tetris, The Legend of Zelda, and Dwarf Fortress to teleporting crazily all over the screen, to the background being Jim Carrey in the "Night at the Roxbury" skit, to pleading for help on Nifflas' forums and Juni climbing a giant version of herself, all while Haddaway's What Is Love? plays in a loop in background. It also spun off countless imitators.
In LISA, Joy is said to have hallucinatory effects, Allowing the user to feel nothing while driving the user to search out the thing they desire most. Brad often has flash backs and sees hallucinations throughout the game and is even hinted to have severe effects on his motives and psyche.
In stage 3 of Lollipop Chainsaw, a local farm is taken over by a psychadelia-themed Dark Purveyor. Juliet will occasionally run across a giant mushroom that she needs to cut down to progress, and each time it triggers a trippy battle against a giant zombie chicken monster, followed by a minigame where you run over zombies with a combine while Dead or Alive's "You Spin Me 'Round" plays. Then after you beat the boss, you find out the whole stage was just a hallucination caused by the boss's powers.
In the Water Works area, there are some giant toads who produce secretions that cause the player's character to have "hallucinations," wherein the screen colors change and there are other visual effects. And you don't even have to lick the toads. (In addition, the mouseover text for the debuff icon says something like "You can taste rectangles and smell the color magenta.")
One of the quests in Evendim involves sneaking a mixture into some giants' cookpot, after which they start hallucinating that millions of spiders are coming out of the woods.
Not even Mario & Luigi: Dream Team was immune to this trope. The "magic water spring" creates this which leads into a faked game over. It heals you as well for some reason...
Mentioned in Mass Effect 2 if a female Shepard romances Thane: if you talk with Mordin, he'll tell you that drell skin secretions have a hallucinogenic effect on humans and warn you not to, um, swallow.
Max Payne has two levels spent in drug-induced nightmares. Once is when Mona knocks Max out with a spiked drink so she can go after and kill mob boss Angelo Punchinello herself, and later when the Big Bad forcibly administers to him a shot of the drug Valkyr and leaves him as a fall guy for the police, covering up her (and by extension her company's) involvement with Punchinello's mafia, though unfortunately for her Max wakes up in time to make his escape.
The Strawberry Fields dirty trick in Mutant Football League; the defense spikes the offense's water, resulting in slowed movement, reversed controls, a wavy effect and psychadelic colors. The commentators can sometimes be affected as well.
Junior: Okay this isn't funny guys I swear to drunk I'm not God but seriously stay in drugs, eat school, and don't do vegetables! Bricks: Uhhhh, Junior's having a flashback, Grim, what do we do?! Grim: Down him talk so he out it comes of. Bricks: Uhhh... Yeah! You're right!
NetHack has a hallucination status effect caused by (among other things) eating violet or yellow fungus, getting zapped by a black light, or drinking a potion of hallucination. It randomizes the appearance of every creature and item in the dungeon every time you take a step, and causes just about every in-game message to be rewritten in Surfer Dude speak.
The canonical explanation for all the Bad Ends in Persona 5 caused by failing to complete Palaces within the time limit is that they're false memories caused by the drugs the police administered to Joker as part of their Cold-Blooded Torture. Except the part where he gets shot in the head.
In Pillars of Eternity, Zahua's personal quest has him and the rest of your party partaking of his stash so you can join him on a Vision Quest.
Allure Seeds in Pokémon Mystery Dungeon: Red/Blue Rescue Team and X-Eye Seeds in the sequel games had this effect — if the character eats one then all Pokémon in the room become strange green doll-like thingsnote Substitute dolls and all items, Wonder Tiles, and stairs turn into flowers until the effect wears off.
The Fairy Ring in Quest for Glory I is comprised of Magic Mushrooms. Consuming them will cause the screen to change colors, with descriptions of the hallucinations ("Wow! Look at all the nice paisley horses! Not to mention the beautiful neon sky."). The first time you eat the mushrooms, you're warned not to repeat it. If you do, the hallucinations resume, and "your mind permanently warped, you die a garishly polka-dotted death."
A very similar thing happens when you smoke Salim the Apothecary's hookah in Quest for Glory III
Rise of the Triad had a mushroom-shaped "power up" that put you in Shrooms Mode, causing most items (including the bad guys, fired missiles, and spring pads) to have a pulsating glow and the player's view to rapidly shift up and down. One of the game's secret levels was a big room filled with nothing but shrooms and spring pads, leading to some whacked out bouncy fun.
In The Saints Row 2 mission "Bad Trip", the Boss is doped to the gills for a meeting with the Sons of Samedi, and has to survive the mission under the influence, which here means "with blurry and tilted vision". It's also possible to drink alcohol (same result as the drug from the above mission) and smoke blunts (screen is covered in fog) whenever you want, though taking more than two at a time tends to hinder the player character in addition to the Interface Screw (too many blunts causes the Boss to randomly stop and cough up smoke, for example).
In the Saints Row: The Third mission "Pimps Up, Hos Down", the Boss is smuggled into Safeword (a BDSM club owned by the Morningstar gang) as a new sex worker, and ends up fighting their way through hordes of enemies alongside Zimos, all while drugged-up and buck-naked.
The Boss (Female Voice 1): It's like living inside a rainbow!
Saints Row IV continues the proud tradition in Shaundi's Loyalty Mission: after scoring a new alien drug, the Boss and Shaundi (both of them) partake in it — and discover that it gave them actual superpowers. They proceed to complete the rest of the mission with their newfound powers while still tripping wildly (e.g. the Boss keeps seeing deadly enemies as colorful furries).
Several of the mission maps are hallucinatory prisons for the gang members The Boss is trying to rescue, in any event. Kinzie Kenzington may very well try to kill The Boss if he ever described what she was stuck in. I'll never try it, so that's a maybe.
Spider-Man (PS4): At one point when he heads to Central Park, Spider-Man gets ambushed by Scorpion who uses the surprise attack to graze Spidey with his poisonous tail. When Spider-Man wakes up from the initial bout of unconsciousness... all of New York appears to be flooded with poison, forcing the player to swing through the hallucinations and hunt down components for an antidote while avoiding giant Scorpion tails inexplicably arising from the sea of poison, navigating through broken pathways, and talking to hallucinations of Scorpion and Otto Octavius on the way. When he finally gets together the components for an antidote, puts them together in the lab, and administers it to himself, Peter finds that he's actually almost completely nude, except for his Spider-Man mask and his boxers.
In the game Sprung, in Brett's story, a hippie character gets him to eat some mushrooms for a 'ceremony'. It leads him to hallucinate loud flashing colours, come up with bizarre game overs, and visualise the hippie as a cow. Slowbeef's Let's Play of the scene gives Brett some surreal No Fourth Wall dialogue during the scene, even cribbing lines from other Intoxication Ensues and Mind Screw scenes as homage.
In Stardew Valley, after the local wizard gives the player character a dose of his brew to make them "one with the forest," dancing leaves and pine trees appear on the screen for a few seconds.
Struggling has the Troy go through one of these, in which he navigates a weird Sugar Bowl full of singing mushrooms, play basketball against a group of buff ducks, and take down another giant duck, Shadow of the Colossus-style.
Touhou Project canon itself has suggested that the magic mushrooms Marisa gathers from the Forest of Magic to power her spells are, in fact, "magic" mushrooms. Or possibly both.
In Tyranny, if the Fatebinder has a good enough rapport with Lantry, they can convince Lantry to let them try Lantry's inks — all of which have at least some psychadelic effects. Red serves as a stimulant of some sort, sepia delivers a marijuana-like effect, and cerulean best fits the trope as it induces synesthesia and bizarre, medium-painting visions.
While under the effects of Talbot's drug, Cutter comments that he sees floors and walls melting. When Drake is injected with the same substance later on, we get to see its effects from his perspective: his perceptions and sense of reality get distorted, with people becoming two-dimensional flat figures as Nate wanders through narrow alleys.
Chapter 21 is an extended hallucination sequence where Drake witnesses Sully's death, runs through the streets of Cartagena while being pursued by spiders, is attacked by flaming demons, and sees himself being strangled by his own reflection.
Waz Hack makes the screen go a glowing, wavy yellow and every living or dead being except yourself looks like a random geometric shape. Also, the random messages on the walls, which normally look like illegible scribbling even though your character can read them just fine, change into graffiti which says "IS IT TRUE OR FALSE? YOU'RE NOW TOO FOOLISH TO KNOW FOR SURE."
In We Happy Few, the town of Wellington Wells looks very different if you've been taking your Joy. This is made especially clear in the game's prologue, where the "piñata" Arthur's co-workers are pummeling turns out to be a dead rat. And then they devour its putrid flesh with every sign of enjoyment.
The Wolf and the Waves: Blue mushrooms are explicitly mentioned to be hallucinogenic. Eating one gives you an out-of-body experience that lets you explore the island as a ghost.
Wolfenstein: The New Order: In the Wyatt Alternate Timeline, protagonist B.J. Blazkowicz, while playing guitar with Jimmy Hendricks, gets given a drop of a red substance by him that puts B.J on a rainbow filled trip.
In the World of Warcraft various alcoholic beverages (particularly during brewfest) can cause many different effects, from seeing pink elephants everywhere to seeing yourself swarmed by gnomes.
Wynncraft has the Shattered Minds quest, where an elf sends you to get a special mushroom. You subsequently get high as a kite and spend the majority of the quest on what can be best described as a drug trip.
Yoshi's Island has an infamous level called "Touch Fuzzy, Get Dizzy." Touching one of the fuzzy monsters that float around in the area will cause Yoshi to stumble around like a drunkard for a minute, distorting the music and the game screen.
Stages 4-1 and 6-3 also have the Fuzzies, so be prepared for some Interface Screw in those stages, too.
MFGG user gamester has made a series of fan games based on the above mentioned "Touch Fuzzy, Get Dizzy," featuring Mario, Toad, and Luigi, all feeling the effects of touching fuzzy (or, in Luigi's case, a fuzzy mushroom.)
ZAngband grants monsters new names so you don't know what you're fighting — the names change every turn along with the appearance of the monster, and run along the lines of Cosmic Horror, Incredible Lovemaking Robot, and so on.
blaring in the background.