We were playtesting tonight and this question came up. My friend flipped Imprisoned in the Source, naming Death's Embrace. If I had a copy of Death's Embrace in my hand, at what point would I put it on the chain to get the effect, the flipping or the naming?

Imprisoned in the Source

Chose the name of a non Team Up plot twist from an opponent's resource row or KO'd pile.
Ongoing
Players can't play cards with that name while you control a Revenge Squad character.

The card name is chosen on resolution. Once the card is named, you're shut out. You can, however, play in response prior to the effect resolving and card being named.

Awesome, thanks.

This goes with null time zone as well