Wave Imp Evolution Quest

Go see Tannah in the obsidian tower and be prepared to fight. Bring friends as I doubt you can win alone. As soon as you enter and she notices a dti, she'll talk and then summon 2 Earth Elementals to help her fight you. When she summons, an Orb of Silt will appear upon her. Loot it from her corpse after she dies. To evolve, you have to give it to Vincent when you're level 250. Unfortunately, it is a ticket item so you cannot save with it. So it is propbably best to do it after you hit 250.

Note with the changes to ofcol and surrounding areas this information is possibly out of date.