Adventures of Lolo/YMMV

Anticlimax Boss: The Great Devil in the first game; after clearing the 50th stage, Lolo defeats him in a cutscene. His reappearance in the second game is upgraded into a proper boss battle.
Ear Worm:
- The main theme will not leave your head EVER.
- Even more Egregious in Adventures of Lolo 3, which has multiple overworld and pre-level themes (both of which combined make up about 5% of the game), but still only one level theme.
- The Japanese Eggerland games have several level themes which can be this. Especially the water/tropical-themed stages.
That One Level:
- The first Castle room in 2, already a tricky puzzle requiring lots and lots of absolute precision and finding blind spots to hide from the two Don Medusae at the top of the room, except there's also a roving Rocky wandering around and constantly getting in the way.
- Many, many levels in III, which expect you know about and exploit various quirks in the engine. so we might as well explain some of them right here:
  - Magic shots take time to travel from one side of the screen to the other, so you can theoretically shoot an enemy trapped in an egg that's blocking a Medusa, and then get out of the way before the Medusa can see you.
  - Pushing an egg halfway into the water will make it slip all the way in on its own. This is important because a stationary Medusa can only kill you if you're all the way on a square.
  - Gols can only shoot one fireball at a time, and can't shoot another one until the first one is off the screen.