x2
-20Sound Veil
When you play this Pokémon from your hand to evolve 1 of your Pokémon during your turn, you may prevent all effects of your opponent’s attacks, including damage, done to this Pokémon until the end of your opponent’s next turn.
Severe PoisonYour opponent’s Active Pokémon is now Poisoned. Put 4 damage counters instead of 1 on that Pokémon between turns.
If I had used Muk & Alolan Muk GX's "Severe Poison" attack that places extra Poison damage counters and in the next turn use Koga's Trap, do they still place the extra Poison damage?
No, they don't. The new, normal Poison Special Condition replaces the old Severe Poison Special Condition.
If I Switch my Active Pokemon that is affected by Poison from Muk & Alolan Muk GX's "Severe Poison" attack and Dust Island is in play, does my new Active Pokemon take the extra damage counters?
Yes, it does. Dust Island specifies that it is affected by "that Special Condition".