S12E17 - The Missing Bone
Synopsis
Trent is called to see Principal Randall, who quizzes him on his current behavior and state of mind, trying to gauge his status without revealing her identity as Elsa. The results are not what she had hoped.
With Dr. Oliver "on sick leave" (due to his demorphing troubles), Dr. Anton Mercer, Trent's adoptive father and alter ego of Mesogog, is brought in by Randall as the substitute science teacher. He immediately stages a field trip to the Reefside Museum he owns (as seen in "Day of the Dino"). There Kira spots a Tyrannodrone, which leads her to storage room where she is forced to submit to the will of a hypnotic dinosaur skull. The creature gives her a sour attitude towards her friends, and ultimately leads her to Tommy's lab to steal a bone she had recently noticed while helping him take inventory. The bone is revealed to be the final component of Fossilador, a hypnotic dinosaur monster created by Tommy and Mercer years ago.
The missing bone fully reanimates Fossilador, and Kira is freed from her brainwashing. Fossilador attacks the city, Black Ranger faces Zeltrax and the Triptoids, and the Rangers destroy Fossilador by destroying the very bone which reanimated him. Back on the island fortress, Mercer desperately searches for a cure for his saurian affliction, but before he can test a new serum on himself, he transforms back to a scolding Mesogog before our eyes.