first edition mewtwo card [1st Edition] #10 Prices | Pokemon Base Set done to Mewtwo during opponents next turn. Mewtwo · Base Set First

I assumed it meant that it would do 120 damage to whatever Pokemon is in the active spot for your opponent at the time so even if they switch, whatever Pokemon they switch into would take damage which still is pretty bad but this is just awful

The same is true for any counters that change its power and/or toughness and effects that switch its power and toughness

You can only use each of the following effects of "Drytron Meteonis Quadrantids" once per turn

[On K type Characters gain +4 cost until the end of your opponent's next End Phase

At this point theyre common enough in Modern that youll need to understand how they work in order to succeed