I've seen some in Purity Forest.Doom seed aka Unfortunate seed lowers your level by one. Its actually very helpful outside of a dungeon. Let's say you're a Torchic at level 34.When you go to level 35 you evolve into a combusken using the cave.At level 36, you then evolve into a Blaziken by going to the cave again.But WAIT!You didn't learn Blaze Kick because Combusken levelled to level 36 not Blaziken.So what you do is eat a Doom seed as a Blaziken and it lowers you to level 35.Then you get to level 36 and you learn Blaze Kick.