Can dominant cards be played whenever? Even during your opponents move?
They can be played at any time, except while a special ability is being carried out or resolved.
For example, if you have used Holy Grail once, and you use it a second time (which discards it), your opponent can't play Destruction of Nehushtan to stop it, since by the time Holy Grail's ability is carried out, it is in the discard pile and can't be targeted by DoN.
