- Demonic Spiders: The Mama Spiders. If you're close, they use an extremely damaging bite. If you're far away, they use a slightly less damaging acid spit. And when you kill them, they spawn dozens of Eensy Weensies.
- Deadheads in Sleepless Hollow. They're fast, they're relentless, they hit hard, and worst of all, when you kill one it just gets back up. (Unless you stand on top of their bodies before they revive or kill them in the light, neither of which is ever mentioned in-game.)
- Shocking Horrors can teleport, move through walls, and drain your life in seconds with their electric attacks.
- Goddamn Bats: Both the Scary Bats and Eensy Weensies in spades, due to their speed and evasiveness. Eensy Weensies are especially bad due to being so small.
- That One Achievement: Several of Supreme with Cheese and Sleepless Hollow's Gallery Goals are this.
- World Peace in Supreme with Cheese requires you to donate 60,000 coins to build a statue, in a game where you get a max of 500 coins per level, and will most likely get double-digit numbers of coins on average. And there's plenty of other stuff to buy in the SpisMall, too.
- Emergency Supplies in Sleepless Hollow requires you to have all 100 candles on hand. If you collect all 100, but spend any of them, you're not getting the goal. Even if you know this ahead of time, you still have to solve some of the game's nastiest puzzles, track down every Last Lousy Point, and do all of it without any of the upgrades from Mr. Klein, making an already hard game even harder.
- That One Boss: Rafe Lector from Sleepless Hollow. As the name implies, he reflects all projectiles, and the only way to kill him is to summon Funnybone and have him kick him to death. Assuming you can actually find the sweet spot where he'll do his kick, move out of the way of Rafe's extremely fast and extremely damaging melee attack without moving Funnybone out of the sweet spot, and kill the Glass Jaws he summons without hitting Rafe by mistake and getting hit by your reflected projectiles.
- Sir Spookly Hauntmore from the same game switches between the normal world and the Dumb Zone when you do enough damage to him. He wouldn't be that bad if he wasn't constantly regenerating health, meaning that by the time you've recovered enough energy to go back into the Dumb Zone, he's probably healed away all the damage you've done.
- That One Level:
- Spooky Castle has The Chase. There's a Super Zombie chasing after you, and you only get 4 guns to kill it with. There's very little room for error.
- Sleepless Hollow, being the Sequel Difficulty Spike that it is, is full of these.
- The Tomb of Darkness is probably the worst. As the name suggests, it's very dark, making it hard to navigate, it's full of the aforementioned Deadheads, and it has several of the game's hardest puzzles.
- The Tomb of Sparks is full of sliding object puzzles and block pushing puzzles, made worse by the fact that solving each section of the tomb activates an extremely damaging laser turret in each of the main hallways, making it even more of a pain to navigate. And to top it all off, you're being harassed by Shocking Horrors the whole time.
- That One Puzzle:
- Most of the difficulty in Sleepless Hollow comes from these.
- The Reflecting Pond from Tomb of Mirrors. Stepping on a switch spawns two clones of Bouapha, and you have to maneuver all three of them through a series of narrow paths surrounded by instant-death water. Most of the difficulty comes from figuring out how much of Bouapha's model can overlap the water tiles without actually drowning, which is much harder than it sounds. And if you exit the room before collecting the candle in it, or die in the next room without hitting the switch in it that activates a Door to Before? You get to do it again.
- The rhythm game in the Tomb of Din. Tiles are falling from the top of the screen a la Guitar Hero, and you have to stand on the corresponding tiles in the room when they pass a certain row at the bottom of the screen. Even if you're good at rhythm games, maneuvering Bouapha onto the right tiles is much harder than just hitting the right button at the right time. And one of the Gallery Goals requires you to hit 30 notes in a row.
- The same dungeon has the five bat puzzle. You have to move five Scaredy Bats, who move away from you when you get too close, onto five tiles arranged in a star-shaped pattern. Getting all five of them arranged onto the right tiles without getting too close to any of the other ones and pushing them away is extremely difficult. And worst of all, the hammer you get as a reward only appears as long as all five of them are on the tiles. If you just try to walk over and get it instead of summoning Funnybone and having him get it, you'll scare them off and have to do the whole puzzle all over again.
- The Tomb of Darkness has two:
- One of the puzzles requires you to walk over a long, winding, narrow path in a pitch black room, surrounded by mud that rapidly drains your health and kills you in a few seconds if you stand on it. Before you enter the room, the path lights up a section at a time, and goes dark once you step in. Unless you have an insanely good memory (or just cheese it by using the Flamebringer to light up the path), expect to die. A lot.
- Another one requires you to guide a rapidly moving barrel through a maze and into a gate. The controls are very stiff, and it's very easy to accidentally guide it into a wall by pressing a direction just a little too late or too early.
YMMV / Adventures of Bouapha