Revealing mistake: When Wolf Jackson touches a headstone as he and the police are about to raid the church, you can see the headstone wobble when his hand lightly touches it, revealing it to be made of a soft, perhaps Styrofoam-like material and not a real headstone.
Revealing mistake: In the second half of his fight with the TVA weaponizing Logan's spoils, Deadpool at one point accidentally stabs himself in one arm using Wolverine's claws. The claws are stuck and hard to pull out, and we are just a few seconds away from a prolonged visual gag based on that concept. However, in this circumstance, the claws come out effortlessly at an impossible angle as he spins away and they do not leave a mark on the suit.
Revealing mistake: In the first scene, they skid around a corner; there are many other skid marks on the same corner from previous takes.