ANNO: Mutationem: One of the various enemies are Mooks wearing metallic armor who'll do a charged rush by ramming with their head.
Akatsuki Blitzkampf: Fritz weaponizes this in his Throw by taking a step forward, grabbing the opponent by the collar, and swiftly headbutting him/her.
Asura's Wrath: Asura is quite fond of headbutting, resorting to it along with his kicks when he loses his arms at several points in the game. As Asura is a frigging demigod and the embodiment of wrath, his headbutts are incredibly powerful.
Battle for Wesnoth: Drake Thrashers are Drake Clashers who have leveled up and gain a third way of attack called "ram", which their unit description describe as using their helmet and skull as weapons.
BattleTech: BattleMechs without fully articulated arms, such as the ancestral Blackjack the Player Character starts with, sometimes headbutt their opponents if ordered to perform a melee attack. In spite of hitting steel armor with cockpit glass, this does not damage the cockpit.
Beyond Good & Evil: Double H does this frequently, although he prefers to put on a helmet first.
Bonk: Bonk's signature attack, as he is about 70% head by volume. He will either whack the enemy next to him with a headbutt, or jump in the air and land head first in a Ground Pound that looks like it would be hard on the neck.
Bravoman has this as his crouching attack, where he shoots out his head like a jack-in-the-box. This is due to his special power of Extendable Arms extending to his neck and legs as well. Weird, but hey, it works.
Castlevania II: Simon's Quest: Subverted. One of the townspeople tells Simon to "HIT DEBORAH CLIFF WITH YOUR HEAD TO MAKE A HOLE", This is a lie.
Dawn of the Dragons: In the second story level, the dragon Solus uses his head as a makeshift Battering Ram to break down the wooden gates of a bandit camp.
In Dead Rising 2, there are three "helmet" weapons Chuck can use to headbutt zombies with. There's the Moose Head, which uses the moose's antlers to ram into zombies, the Burning Skull which is similar but with bull horns and the Super Slicer which combines this trope with Helicopter Blender; slicing zombies with its propeller.
Dead Space 3: Divider heads are disembodied heads that scamper around on tentacles; if they find a human corpse, they'll replace its head and take up residence, directing the body to murder the player. Sometimes, the monsters will remove their own heads and lob them at Isaac, initiating a grapple sequence where the head attempts to replace Isaac's head with their own.
Defenders of Dynatron City: Toolbox attacks with his hammer-shaped head, but it has pitifully short range. Team leader Jet Headstrong does, too, but his is rocket-powered, making him a bit more useful.
Demon's Crest: Although not an attack, Firebrand headbutts objects in the background to find money and Upgrade Artifacts.
Destiny 2: The Exotic Titan Helmet "An Insormountable Skullfort" states as much in its Combat Instructives: "Your skull is now a mighty bastion. You can break anything with your skull. [...] You enemies do not have a skull fortress. Their skulls are like meadows. Play in the meadows."
Also in the Destiny setting, there's Saint-14, who in the backstory caved in the skull of the Devil Kell with a headbutt. When we meet Saint-14 in the present day, he makes his return by headbutting a Vex Minotaur repeatedly until its casing finally cracks.
Dwarf Fortress: One mod allows dwarves to do this. Such an attack can easily send a human warrior skidding five feet across the ground, breaking bones with each bounce, which tends to do a lot more harm than the headbutt itself (which can smash bits of skull through the aforementioned warrior's brain even with a helmet, mind you).
Dynamite Headdy has a default attack which involves launching his head forwards or upwards to damage enemies, shown neatly on the box art. It's never stated how or why, but he's meant to be some kind of puppet or toy so it's highly unlikely to inconveience him.
Dynasty Warriors has badass bodyguard Dian Wei, whose running attack for the longest time was a charging headbutt. This can send enemy officers flying and will result in a Foe-Tossing Charge if steered into a crowd of Mooks. Fittingly, he's bald and in the opening for the fourth installment of the game, is depicted headbutting a boulder to pieces and wiping the rock dust off his head with a smug grin.
Earthworm Jim offers an interesting variation of this trope: Since the player is essentially a (freakishly large) earthworm in a humanoid exoskeleton Power Armor, you can actually use your wormy head to whip your enemies and as a propeller to slow down a long descent. In the sequel though, Jim gains the Snott Parachute because last game's Helicopter Head made him quite dizzy and left him with some severe lower back pain.
The Elder Scrolls IV: Oblivion: Minotaurs have the head ram as their ultimate attack. It's actually quite powerful, thanks to their horns... and the little fact that it is always coupled with a magical strike that disintegrates your armor and damages your health directly.
In Final Fight, Mike Hagar can do this when he grapples with an enemy. The fat Mooks in the first game use charging headbutts.
In For Honor, headbutts are a common attack among the Viking classes, with the Warlord having it as an unblockable that can knock back his opponents. The Valkyrie can also headbutt her opponent in a couple of her executions. The Shugoki, a Samurai class, can also use a headbutt as a followup to any light or heavy attack, and doing so knocks his opponent back very far, drains half their stamina bar, and stuns them, disabling their HUD briefly.
Shuju, one of the earlier bosses from Gekido, attacks exclusively by headbutting, by prepping himself for a charging tackle across the area and trying to ram his scalp into you for huge damage.
The Godfather 2: You can do this to enemies you're grabbing.
Head Panic: Throwing your detachable head at enemies is your main form of attack.
In Killer7, Mask De Smith stops a bullet by headbutting it out of the air.
The Legend of Zelda: Link's Awakening: Since The Turtle Rock's head is the only part of its body that can move, it tries to kill Link by aggressively headbutting him.
One of Kiryu's many Heat moves in the Like a Dragon series is to grab an opponent by the collar, soften their face up with a couple of punches, before smashing his forehead into their face for the finishing blow.
In Yakuza 2 and its remake, the heroes need to access the Florist's underground security system in Purgatory, but it's offline. Majima then strolls in and begins repeatedly bashing his head against the desk (while wearing a construction safety helmet) until it turns back on and brings them down.
The Lost Vikings: Erik the Swift's power is head-butting enemies and breakable obstacles.
Marvel's Spider-Man 2: At one point, when an enemy tries to grab MJ from behind, she slams her head backwards into their nose. It's played fairly realistically in that it doesn't do much beyond disorienting them long enough for her to use a more effective means of fighting them off, and afterward she's shown wincing and in pain from doing so.
In the Marvel vs. Capcom series, there's Juggernaut's "Juggernaut Headcrush" Limit Break, where Juggernaut races at his opponent head first like a battering ram.
This is how krogan tell each other to "shut up", as a display of dominance. In Mass Effect 2 you have a Renegade Interrupt that allows you to do this to the obnoxious Uvenk, which not only is successful in getting him to back down, but leaves him a little dazed afterwards.
Shaman:[laughs] I like this human! S/he understands!
Matriarch Aethyta (Liara's "father") assures her that, since her grandfather was a krogan, it's perfectly natural if she ever feels the need to headbutt someone. And indeed, Aethyta herself can be seen in a Shadow Broker video headbutting an uncooperative krogan, with the krogan clearly suffering more harm for it.
In the second game, after Shepard & Garrus interrogate Harkin for a bit, Garrus pulls out a pistol to shoot Harkin in the leg. If you take the Paragon Interrupt, telling him he doesn't have to shoot the guy now that they've got what they want, Harkin tries to act all cool... only for Garrus to floor him with a headbutt.
Drack recounts the time he headbutted a vehicle for giving him a funny look. At one point in the game, his teammate Liam can be heard trying to convince Drack to let Liam headbutt him For Science!. He's talked out of it, but a drunken idiot on Kadara is not so lucky.
Pathfinder Ryder can threaten to do this to a pair of krogan guards at the door to their colony. While they don't get the chance, it does impress the guards a lot more than Ryder simply trying to be civil does.
Metal Gear Solid 4: Guns of the Patriots" Liquid Ocelot does this a few times with Snake, and they end up doing it to each other as well. Snake can also score a few headbutts on Liquid during the boss battle.
The Barroth uses this as its signature form of attack, and it hurts about as much as one might expect, coming from a thick-headed, nine-foot tall dinosaur running at what's probably around 40 miles per hour. It also flips you into the air on impact for extra measure.
There's also the Uragaan, which features a rather unique take on the trope. Rather than attempting to headbutt enemies with its armored forehead, it will instead use its thick, reinforced lower jaw to smash hunters into the ground, known in some circles as the "Jay Leno Smash."
Mortal Kombat: Some characters have headbutts in their moveset.
Kano has a weird sort of short headbutt in the sprite-based games, justified by having a metal plate installed in a fair portion of his face and head.
In one of the weirdest instances of this trope, particularly for a fighting game, there is a challenge mission that causes all of your limbs to fly off at your opponent the instant you make an attack. This includes flinging your own head at an enemy to headbutt them from across the screen. Bizarre does not begin to cover it.
Ōkami: A favored tactic of Amaterasu's. Useful for breaking pots, defeating Imps, getting other people's attention... She's a wolf, you know.
One Must Fall 2097 features the Shredder, a mining robot with clawed hands and a large mining saw on the top of its head, giving it a slightly punk-mohawk look. One of its moves involves throwing itself headfirst at an enemy with its head-saw active, which of course does considerable damage to the other robot and leaves the Shredder itself unharmed. Advanced players can chain up to three of these together, among other insane combos.
The attack Skull Bash works in exactly this manner, as well as Headbutt, Head Smash, Iron Head and Zen Headbutt. However, Head Smash actually hurts the user.
In addition to that, Cranidos and Rampardos are Pokémon based around this trope. Like many Pokémon, this was based on a real animal, albeit one that was recently determined not to have used its head quite as much as was originally thought.
Scraggy and its evolution Scrafty are thematically very focused on using their craniums as blunt weapons.
Pokémon Mystery Dungeon: Many Pokémon with short arms in Pokémon Dungeon: Gates to Infinity use a headbutt as an attacking animation for some of their physical moves. Not all of them actually learn the move Headbutt, however.
Power Rangers: Fighting Edition features the Shogun Megazord, whose throw involves grabbing its opponent and slamming them against its spiked helmet. This hurts like the dickens, and sometimes puts foes into a Cycle of Hurting because it causes them to fall just close enough for the Shogun Megazord to plod over, grab them, and do it all again.
Primal Carnage: Bruiser class dinosaurs have the ability to attack simply by running into humans at high speeds. This varies slightly between the three different species. The Carnotaurus does the most damage and has the temporary ability to regain health every time it damages something, but it has awful turning, the Pachycephalosaurus has less health and does the least amount of damage, but it's much more agile and has a bulletproof skull, while the Ceratosaurus is the most durable, but it's the slowest and has the least stamina (which is partly offset by a temporary ability to leech stamina from humans it damages).
Ristar uses this as his primary attack. On everything.
In River City Ransom, Ivan, who attacks outside the high school, can use a fairly powerful headbutt.
Keiji takes out both Ieyasu and Mitsunari with headbutts when they refuse to stop fighting and listen to him.
Solomon's Key: Dana can break blocks by butting into them from below.
Spyro the Dragon: One of Spyro's main ways of dealing with enemies is to charge them with his horns, especially ones that are wearing flame proof armor. Loot Chests can be smashed open as well.
Balrog, in all of his incarnations, always has a move that involves grabbing his opponents and headbutting them multiple times. It's even lampshaded in SNK vs. Capcom: SVC Chaos:
Mr. Karate: You should train your head too, big boy. Balrog: My headbutts are a work of art, eh?
E. Honda has this, ever since his debut, as a special maneuver. Note that in-game graphics always show him as flying head-first like a kamikaze Superman, but one piece of art tried to pass it off as a shoulder ram. No-one's buying that, Capcom.
Also Dhalsim, who starts with a normal headbutt attack and then uses headbutts as a drill-like Ultra move, the Yoga Shangri-La.
Alex's super Stun Gun Headbutt is an example. This chain of headbutts can stun his opponents.
Mario and Luigi are frequently mistaken to be breaking overhead blocks by headbutting them, but are actually hitting them with fists.
In the Super Smash Bros.. series, several fighters use their heads as some form of attack. While most instances of this are only about one or two moves, Yoshi uses almost only headbutt-related moves when on the ground, as his arms are too short to effectively punch.
For that matter, Luigi's side-B move, Green Missile, is basically a charge-up attack with which he launches himself head-first at an opponent. It's even possible for him to get jammed into walls this way, given enough force.
In Super Mario RPG, give Bowser the Hurly Gloves and watch him take his frustrations with Mario out on the enemies, even if Mario is at 0 HP!
In Tales from the Borderlands at one point, Rhys' corporate rival Vasquez tries to headbutt him in the face, both to curb his sass and to assert male dominance, but he ends up hurting himself as much as Rhys, if not more. Jack openly criticizes his form, asserting that you should always aim your forehead for the bridge of the other person's nose.
Tales of Maj'Eyal: Certain classes can learn the Skull Cracker talent. Other classes can learn it by wearing headgear with certain ego bonuses. There is even an achievement for defeating a certain number of bosses using this move.
Every Mishima note Yes, Jinpachi, Heihachi, Kazuya, Jin (was the case for the first Tag title, now specific to Devil Jin), even Lars has this move. Though Lee doesn't.) has Stonehead as a throw. As you might guess it's a headbutt throw. Heihachi can also slam his head against his opponent as a regular attack (called the "Chrome Dome").
All the animals save for Gon have a headbutt throw.
Heihachi. First, in his Tekken 5 interlude in Story Mode, he headbutts the crap out of Jack-5 after defeating him (in Jack's story mode, he headbutts the stuffing out of Heihachi before punching him into a Twinkle in the Sky despite not having the Stonehead throw). Second, since Tekken 3, he can perform a "Headbutt Carnival". Instead of a regular Stonehead throw, the recipient can reverse the Stonehead and, well, Stonehead him back!
In Tekken Tag Tournament 2, if you have two Mishimas on your team you can perform a tag Stonehead throw.
Craig Marduk has a number of combos that end with a quick headbutt.
Various versions of the Jack robot have had a charging attack that allow them to perform a flying headbutt, E Honda style.
Tomb Raider (2013): A favourite technique of CaptainGrim. He calls it the "Glasgow Kiss" and boasts about using it on the Loch Ness Monster. It foreshadows his last stand later in the game, where he headbutts a goon trying to hold him hostage against Lara, and tries to take out another with a headbutt only for the goon to drag him to his death.
Tori Bash: Do this right and you can bisect your opponent with it without your own head snapping off at the neck. You'll lose a lot of points for doing it, since the game considers it to be a high-scoring 'enemy blow to the head,' but it's still pretty awesome to cleave an opponent in half with your skull.
Total Overdose: One of Ram's loco moves allows him to live up to his name, charging like a bull at double maximum running speed with his head down and fingers pointed forward like horns. Any non-Boss enemy hit by it is thrown in the air, and dies on landing. One battle in particular encourages its use by leaving the appropriate pickups scattered around, and takes place in the middle of a bullfight arena.
Touhou Project: Keine Kamishirasawa is known for headbutting students who don't do their homework. On top of that, she's a Were-Hakutaku, meaning you really don't want to piss her off on the days of full moons — there's a reason fans of the franchise refer to this as getting CAVED.
The main attack of the Moai head in Wai Wai World is swinging its head forward, which can also break blocks.
In The Walking Dead: The Final Season, Clementine wins the struggle over a gun against Minerva in the Episode 4 by knocking her down with a headbutt.
Wario World: Red Brief J uses a head-first charge as his primary attack. (Which makes sense when you consider that he's a big bull.) The number of charges he can make with each attack is equal to five minus the number of Health Counters he has remaining. This attack is actually his weakness; he's immune to all of Wario's attacks, but if Wario dodges all of his charges, he'll be dizzy for a few seconds, and can be dunked in the lava surrounding the arena if Wario does a Ground Pound on the center. This costs Red Brief J one Health Counter, but each one makes him angrier and stronger.
to crush your enemy's face with your skull.