Moonlight Stadium/Umbreon vs Ariados

[Xaej]

If I have Umbreon on my bench, a Leafeon lv X active and there is a benched Ariados, which effect takes place first?

A)

Umbreon gives Leafeon lv X 0 retreat, then Ariados increases that by 1.

B)

Ariados makes Leafeon lv X's retreat 3, then Umbreon makes it 0.

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Same with Moonlight.

Active Bronzong, Moonlight Stadium out, benched Ariados.

Thanks in advance!

 

[PokePop]

per the rulebook, anything that sets a retreat cost to zero, like Umbreon does, it stays set there.

If it's just addition and subtraction, like with Moonlight stadium, just add and subtract to get the final answer, In this case, it would be +1-2 for a total -1