The White Monster
The White Monster is an unnamed creature that terrorized Jump City when the Teen Titans returned after fighting the Brotherhood of Evil.
The monster can shape-shift it's body into anything it touches, like concrete, water, metal, oil, and fire. The four remaining Teen Titans fought the monster, but were no match without Beast Boy's help (because Beast Boy saw a girl who he thought was Terra). Beast Boy then let the girl go and ran off to help his friends fight the monster. The monster's defeat was never shown (due to the fact that the Teen Titans TV series was cancelled).
Therefore the monster's fate remains unknown.