Pokemon has officially updated their errata document with corrected text for Furious Fists‘s Fighting Stadium and Phantom Forces‘s Jamming Net, which previously used incorrect wording and terminology. Erratas are corrections to cards that must be used whenever you play them. Thus, you must pretend the new wording below is what is printed on the actual cards. Refer to the scans to see the old wording.
The attacks of each Fighting-type Pokemon in play (both yours and your opponent’s) do 20 more damage to the opponent’s Active Pokemon if it is a Pokemon-EX (before applying Weakness and Resistance).
How it was changed: This stadium should only impact the Active Pokemon-EX belonging to the opponent of the attacking Pokemon.
The attacks of the Pokemon this card is attached to do 20 less damage to each of the opponent’s Pokemon (before applying Weakness and Resistance). (Don’t apply Weakness and Resistance for Benched Pokemon.)
How it was changed: This tool should only impact the Pokemon belonging to the opponent of the attacking Pokemon.