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 TV series was cancelled). Therefore the monster's fate remains unknown.
However in 2011, Greg Cipes, the voice of Beast Boy on the show, had stated that work on a new season was underway and that a live action Teen Titans film was planned for release at the end of 2012. In 2012, Derrick Wyatt (animation designer of the series) stated the next arc would feature the Titans setting up international Towers, and battling the monster from the season 5 finale. But as of 2017 there has been no known progress on the series at all and it's unknown if there ever will be.