The move imprison is waaay overpowered, in FFA's particularly.
This single move prevents any pokemon from using the same moves as the user, and with the expanded movepool of the URPG that can be literally an entire pokemons movepool (if it's the same pokemon for example).
My suggestion to make this move less broken are one of or more of three things:
Restrict it to a single target, rather then all pokemon.
Make it so they only can't use those moves against the pokemon that used Imprison (still a bit broken for non-FFAs)
Make it so they choose 4 moves when they use Imprison, and it only applies to those 4 moves.
The third option is closer to the GBA use of the move, since pokemon only have 4 moves (well, 3 moves besides imprison). These are just ideas, and maybe you guys have a better idea or don't think it's broken. But in my opinion it seriously needs to be changed.