This is another version of Beast Boy from Teen Titans, From Teen Titans GO. He was once the original and he was turned into the Go Version by The Joker so the TTG can work for him and ruin The Teen Titans name. He is introduced when Joker and Fang try to capture Bender and they give the location to them when they escape. They also join Joker, Thawne, Fang and Darkwarrior Duck.
Beast Boy is brought with Joker to kill the heroes and he specifically tries to kill Bender with Cyborg being eager to avenge his death at Bender's partner's hands as Joker told him. He then helps Joker's team get the parasites Joker wants and fights his teammate Starfire who easily dispatches of them all.
Robin, Raven and Starfire attack the Legends by suprise which angers Mick espically. Remembering his first encounter with them and decides to light them up, pointing out they need to kill them as long as they exist, Thawne and Joker can use their connection against them, Rip, Sara and Rip disagree with this and fight the three. Mick makes his leave and finds Uka Uka, Terrance Lewis and Cyborg and Uka Uka notices that he's not without his friends and points that it's not worth his time and has Terrance and Cyborg attack Mick. Seeing the radar in Terrance Lewis's hands, he attacks Cyborg and they lock fists until Cyborg tries to use his cannon on Mick, who is knocked back but Mick set adjusts his fire power to overcome the next shot and sends Cyborgs down with Terrance Lewis taking out a cold gun and trys to freeze Mick. Mick wonders where he got the gun from, and Lewis points out he copied the cold gun to use against Mick. Mick throws a beer bottle and sets it on fire which makes a fire circle around Cyborg and Terrance Lewis and makes off with the radar. Before he can get too far The Teen Titans show up and try to force Mick to give up the radar for his friends. Mick has an other idea and offers them a beer, Robin refuses since he's the perfect hero to him, But The others blow him off and take a drink of beer and this is when Mick challenges Raven, Beast Boy and Starfire to drink under him the table which they do. Robin tells them to focus as They need to listen to the Joker and he will be very mad at them. They ignore them and Rip wakes up from being unconsciousness and has Sara and Ray disarm Robin.
Beast Boy continues fighting for Joker until he with Cyborg, Raven and Robin are all wiped out from existence from Toffee who feels that they know too much about him and NOS4a2's plans. He is also torn up about Starfire ditching them for the enemy.