Ruling pixies and skarmory (sp) + ampharos

[pineapple]

if you have attacked with skarmory (sp) the turn before you opponents and have an ampharos in play.
Can your opponent successfully use the pixie's powers??
This can also applay for pokemon that arent {G} or {P} with a Miasma valley in play.
who gets priority?

 

[Rummage]

The pre-existing condition will override the coming into play power.
Ergo, Damage is placed first.. so, for example, uxie's power won't be able to work since it will have damage.