What's the best way to have the pawn move underground?

Is there a way you can change the players position so that it’s model is partly under a floor or completely under a floor?

I want to create a situation where one type of character is walking on the ground normally while another character type would be sunken into the same ground. Is this kind of thing done through collisions or hit-boxes?

A good example of what I’m looking for would be a character that walks on top of a sand floor while the other one is buried waist high in the sand floor as they move.

Do you want the partially underground pawn to still be “walking” on the ground collision, but just appear to be sunken into it? If that’s the case, all you’ll need to do is offset the character’s mesh in the component’s tab so that it’s below the collision capsule, and possibly shrink the capsule a little so it doesn’t extend too far above his head.