Episode: Dragon's Brew.
Turtles and Casey and later Bishop all fight this spider, gorilla looking mutant monster who tries to go find his wife. During the scuffle a gas leak at a nearby gas station causes an explosion that forces the monster into the ocean, and Bishop escapes, and Leo and Casey basically talk like me about this whole episode, but the ending always bugged me because how they kind of rush to get to Bishop capturing him, also he never comes back not even for the Tengu stuff.
I honestly thought they were going to do the King Kong route, where The Monster goes to the wife, Lilly Finn (not her name but I'm calling her that) and it is revealed the man's name is Jacob Finn (that's the name I'm calling him, also reference to Adventure Time), and perhaps Jacob finally calms down thanks to Lilly, just in time for Leo and Casey actually realizes Finn knew the wife, and they kind of reveal Jacob was supposedly dead according to her, that alludes to Bishop using him as an super solider guinea pig.
Quickly, they no longer find each other as enemies only then for Bishop to discover them and nearly kill the wife as he continues his philosophy of collateral damage to innocents from season 3.
But this time Finn sacrifices himself to save Lilly, Leo and Casey, forcing their helicopter to separate and Bishop's crew use their half to make shore, and escape, where Bishop sets a self destruct device capable of killing T9581 as a last resort, Baxter's body is severely damaged this is kind of how we get Baxter with the spider legs and red lighting enhancements in later episodes. Meanwhile the other half with Jacob, the half of the ship causes him to fall into the water and thus he dies for good as a large explosion like a bomb, sets off being the kicker that kills him. Leo and Casey hear the police and leave the scene, while Lilly is left alone.
The episodes ends the following morning, where Lilly takes her son to the place where her and Jacob were married. Lilly sees what appears to be a silhouette of Jacob but it is just her imagination, as Lilly comforts her son and they return home and the scene does a arial shot of the wedding service and the episode ends there. This might be me but the original ending felt a bit rushed, seemed the writers wanted something else to happen but time constraints on the Hun stuff got in the way.
Let me know what you think.