Good Day @Z4ngad0
As @Mysticwind has stated, Trick Room has a -7 priority and with prankster is becomes -6. Specifically, the ability Prankster does not guarantee that non status moves will move first but rather it increases the priority tier by +1. In general, the ability Prankster allows non status moves with a base priority of 0 (such as Memento or Switcheroo) to move before most other moves.
Another instance of this memento used by a Prankster Pokemon not going first if were against a Pokemon using Extreme Speed. In this scenario, Memento would have a +1 priority (boosted by Prankster) while Extreme Speed has a +2 priority.
I hope that this explanation eases your confuses and provided you with a better understanding of how the Prankster interaction works.
Does this answer your concern?
Regards,
Bitterblade