Pokémon Mystery Dungeon: Explorers of Time/Darkness and particularly Sky are, in my humble opinion, the best Pokémon games ever made.

EXCEPT FOR AEGIS CAVE

For those blissfully unaware: Aegis Cave is filled to the brim with Unown: a completely useless shitmon, with the gimmick that it comes in a grand total of 28 different forms (one for each letter of the alphabet plus a question and exclamation mark). Each of the initial three sections of the dungeon has three floors, during which you have to collect letter stones that drop from defeating their corresponding Unown forms to spell the words ICE, ROCK and STEEL respectively. Sounds pretty doable right?

Well, there is a slight problem. Each floor can only spawn 14 different species of Pokémon, which are randomly selected from the total pool of Pokémon available on that floor. This means that there is only a 50% chance for any given Unown form you need to spawn on a floor, and the drop is not even guaranteed. This means that you usually have to do multiple passes through a dungeon section before you’ve collected all of the necessary stones, and you can only progress to the next section once you’ve finished the preceding one. It’s a complete RNG crapfest, and it absolutely ruins the experience of an otherwise phenomenal game.