Both players have 1 prize left. Player-A uses Galarian Slowking V's "Word of Ruin" attack. Player-B attacks Galarian Slowking V with enough damage to KO it with the same Pokemon that got hit by "Word of Ruin". Who wins? Or is it a tie?

The KO from Player-B's attack happens before the end of their turn, so the game is over before Word of Ruin's effect gets to happen. Player-B wins.

Relevant cards

SWSH6_99