I assume my opponent cannot use the effect still, but I wanted to confirm.
The compendium has the ruling for the older text:
Q. Chaos Gym is in play. I play a Plus Power. I flip a tails. Can my opponent use it on their next turn? If not, why? Are there other cards that can't be used?
A. They cannot. Chaos Gym will not let your opponent use trainers that must be put into play. Sorry for confusing you [earlier], that was our mistake in not checking the card text first. (Oct 19, 2000 WotC Chat, Q67 & Q78 & Q81 & Q90)
But with the new errata, I just wanted to confirm this has not changed.
The compendium has the ruling for the older text:
Q. Chaos Gym is in play. I play a Plus Power. I flip a tails. Can my opponent use it on their next turn? If not, why? Are there other cards that can't be used?
A. They cannot. Chaos Gym will not let your opponent use trainers that must be put into play. Sorry for confusing you [earlier], that was our mistake in not checking the card text first. (Oct 19, 2000 WotC Chat, Q67 & Q78 & Q81 & Q90)
But with the new errata, I just wanted to confirm this has not changed.