Tasselworms are people!After the green apple splat meltdown, the workers were kept behind that one side door. After the students left behind went down that corridor, they didn't meet anyone but blue tasselworms. Up until this point, the only tasselworm we saw was the reddish-brown one with t green and yellow sweater. This means that the blue ones are at least different. Plus, the main tasselworm is amazingly sentient, if you are paying attention. Maybe he's even the missing principal!
Lee's dad is RadcirclesHe used to be a great prankster in his high school days, and he set up Lee for the prank partly to force his son to develop his own skills, as well to help him make some friends.
Lee will not be the only one who gets blamed for the second prank.According to the Detentionaire wiki, the third season will begin with Lee getting blamed for yet another prank that was similar to the first one. The perpetrator this time is supposedly a different person. The WMG is that this time, Lee's friends (Biffy, Camillio, Holger, and Tina) will also be accused of being Lee's accomplices. This puts all of them in detention for the rest of the school year, making sneaking around all that much more difficult since none of them will be able to move around as freely anymore. This will also allow Biffy to tag-a-long on missions and leave someone else on sync-watch duty.
Lee's mom will be the new principal.As of the second season finale, Principal Barrage is AWOL and Vice Principal Victoria has been dealt with by the council. That leaves two positions in the school free (not to mention the empty positions left by the missing teachers). Lee's mom becoming the principal could explain how Lee will no longer be expelled.
The council will fulfill all the missing positions at school.As of the end of the second season, four positions need to be filled: The Principal, the Vice Principal, the Coach, and one teacher. The council will infiltrate the school by filling in these positions during the course of Season 3.
Lee's MomUsed to be, or possibly still is a spy.
The SerpentIs actually Lee's long lost brother. His fixation on Lee's family and the resemblance between him and Lee make it suspicious.
The council is working with cloningThe Serpent collected a bandaid and razor from Lee's parents, probably for DNA.
Lee is a Replacement Gold Fish.Going off of the theory that the baby in the picture isn't Lee but another child who was revealed to be the Serpent, they probably had Lee to fill the void.