If my opponent takes a prize and then I use Naganadel GX's "Injection GX" attack to add a prize to my opponent's Prize Cards, would my Dubwool V's "Revenge Blast" attack do only 120 damage because the number of prizes in my opponent's Prize Card area has increased? Or does it do 150 damage (120+30) because the opponent has already taken that prize (even though it is now back in the prize pile)?

Revenge Blast is based on the number of prize cards TAKEN, so even though the Prize Card gets put back into the opponent's area it still counts as +30 damage for Revenge Blast.

Relevant cards

SM11_160

SWSH2_153