The wording of Fighting Stadium is now as follows, "The attacks of each {F} Pokémon in play (both yours and your opponent's) do 20 more damage to the opponent's Active Pokémon if it is a Pokémon-EX (before applying Weakness and Resistance)." This stadium should only impact the Active Pokémon-EX belonging to the opponent of the attacking Pokémon.

Relevant cards