Magic Evens
If Mr. Mime ex would be damaged by an attack, prevent that attack's damage done to Mr. Mime ex if that damage is 20, 40, 60, 80, 100, 120, 140, 160, or 180.
BreakdownCount the number of cards in your opponent's hand. Put that many damage counters on the Defending Pokémon.
When Pokémon-ex has been Knocked Out, your opponent takes 2 Prize cards.
Can Choice Band be used to get around Mr.Mime GX's "Magic Evens" Ability that blocks even amounts of damage?
Yes, the Choice Band and all other effects that may adjust the attack total are factored into the amount of damage being done before Mr.Mime GX's Ability is checked.