thanks for the reply!
the pressure plates have a variable that defines how deep into the ground they should go, i accidently left it as the default 0.7 which led to the plates going into the ground then rising up again because there is no more contact with the rigidbody before going back down again and making a damn mess
I think the reason of the boxes' behaviour is that I forgot to make a physics material for them, (there was already one that had no friction that i placed on the ground and the player so that the player doesn't get stuck on walls but it also led to boxes being slippery)
also, thy skeleton is Azcuth himself, the god of reality. the idea behind his design is that Azcuth was a powerful and feared god, after his death, his body was preserved inside the tomb, but he wasn't really dead. but his body kept rotting so much he had to put away his heart to get charged into another place than his chest, leading to it getting crystalized, which is the artefact many have died searching for