Most useless toon in the game

Grievous is definitely top in term of abysmal return on investment, but not far behind are Geonosian Spy, URrroorrrorr (and until recently Hoth Soldier, Lobot).
Eeth Koth also deserves a mention I think.

Then all the fallen stars, toons that were once great but have returned permanently to the bench: Luminara, Droids,...