If I have multiple Toxtricity with the "Maximum Downer" Ability in play, will my opponent's VMAX Pokemon have -30 HP for each one?
There is no restriction about multiple Maximum Downers being in effect; in other words, yes it stacks.
Maximum Downer




x2Maximum Downer
If all your Pokémon in play are Fusion Strike Pokémon, your opponent's Pokémon VMAX in play get -30 HP.


Head BoltIt has an electrical organ on its chest. While generating electricity, it fills its surroundings with what sounds like the strumming of a bass guitar.
If I have multiple Toxtricity with the "Maximum Downer" Ability in play, will my opponent's VMAX Pokemon have -30 HP for each one?
There is no restriction about multiple Maximum Downers being in effect; in other words, yes it stacks.