I know that Leo is afraid of losing his team, Donnie is afraid of losing April, Sensei is afraid of losing the Turtles, Raph is afraid of cocroaches, and Casey is afraid of rats, but what is Mikey and April afriad of?????
April - Kraang Subprime, who was her "best friend" for a whole year. Finding out your best friend is betraying you and your friends has got to cut. Also, of Donnie and Casey forcing April to choose.
Casey & Donnie - That April may be a player who likes the attention but is unwilling to commit to anyone.
Jason - He's already had a terrible year, but managed to remain positive through it. Who knows what terrible things happened after he mutated and before Xever took him in. It's honestly hard to imagine what he fears.
Karai - That her life in the Foot Clan has left her too with too many bad instincts (such as revenge), and she can only be a danger to her family.
Kirby - Of April maturing into something both terrible and powerful.
Kurtzman - Of them finding him. He won't know how, but they will have found him. :)
Leatherhead - Someday dying of old age and causing Michelangelo more pain.
Leo - For better or for worse, I think his greatest fear now is the Shredder, after he brutally defeated Leo within an inch of his life, and Leo will conquer that fear by being the one to take the Shredder down.
Mikey - It's hard to say. Mikey's the kind of character who doesn't seem to have a deep-seated fear of anything. Even his fear of Squirrelanoids seemed kind of random.
Pete - A world without sourdough.
Raph - My theory is that Raph is a very private person in his relationship with Slash, and doesn't want to his family and friends snooping on it. Of course, since he does get so secretive about it, it makes it all the easier to tease him. So I think Raph fears this kind of ego-smashing scrutiny and invasion of privacy. Also, cockroaches still—I zoomed in, and all those cans in Raph's room are bug spray, not spray paint.
Rockwell - Losing his sentience and intelligence again.
Shredder - Irrelevance, especially in the lives of the people he hates.
Slash - Becoming unstable again.
Splinter - It's hard to say what Splinter fears most, because so many of his worst fears have already happened.