So the manga I'm thinking of is of the mystery genre. It's a bunch of kids (I'm pretty sure) that get locked in a school and they have to solve riddles or something. One of the kids in particular is dressed in a weird cartoon character-esque suit, kinda like Kuma from Persona 4 I think but bigger. The kid inside the suit is a cripple or maybe even dead, I forget. In one of the scenes this kid in the suit has to do something with the giant clock in front of the school on the roof, and they eventually find a door behind it (not sure about this bit). I think the suit gets ripped up by the clock gears as well.

That's all I remember. Sorry if there are any spoilers in this but it's really annoying how I can't remember what manga this is! I trust that someone in this subreddit has read this manga before, so hopefully I can get some help.