Some TMNT stuff really isn't for little kids.
In the IDW continuity, B'een Go is an alien from the planet Go'mo, whom the Ninja Turtles sought as a witness for Krang's trial. However, as Leonardo attempted to convince him to come with them, Hakk-R appeared and told him that the Turtles were assassins. The naive B'een believed him and accompanied the assassin back to his ship, realizing too late what he really was.
Fortunately the Turtles managed to catch up to the ship, and Michelangelo successfully rescued B'een before the Turtles defeated Hakk-R. Realizing that the Turtles were his allies, B'een agreed to testify against Krang.
On the trip back to Neutrino, B'een apparently formed a friendship with Anemon, who promised not to let anything bad happen to him. He was the first of the witnesses to take the stand, relating how Krang had forced him to evaluate the emotions of those he tortured. Unfortunately, his testimony was undermined by Vin-Bini, who argued that the torture was actually "advanced interrogation techniques."
Though seemingly kept in a safe place during the Malignoid attack, B'een detected Hakk-R approaching to kill the witnesses. Fortunately Donatello was able to end this threat, and B'een witnessed the sentencing and death of Krang. After this, he was taken back to his planet by Zak and Kala.
B'een Go is described as a "reclusive and indestructable empath". His abilities make him unable to die so long as he is on his planet. He also changes color based on emotions.