The fewer PP this move has, the more power it has for attack.
Trump Card's base power is dependant on the amount of PP that it has left. Its Base PP is 5 so it can go up to 8 in the amount of Base Power. However, this attack is the one case where using a PP Up or PP Max on it is a bad idea.
There are 5 levels of power that Trump Card has. These are displayed below: