I have a question about Mace Tyrell's card abilities.
The idea of getting power upon paying a coin when a Tyrell character enters play is pretty straight-forward, but I was wondering how it works with the effect of Mace being able to take a character out of play and putting it back in the next phase. Is that character, strictly speaking, entering play or is it the expiration of the removal effect? Therefore, can I pay another coin to gain another gold and use "enter play" effects for, for example, The Hightower or Olenna's Informant?
Considering the quote below, about Barring The Gates, I would think that the character technically doesn't "enter play", but I would like to verify this.
After talking this through with Nate, we would rule that Barring the Gates will not prevent the character from re-entering play, per the rule you cited. Mace’s ability is not causing the character to enter play; rather his ability caused the character to leave play, and the expiration of his effect is returning the character to play.
For an analogous situation, imagine if Barring the Gates read: "Card abilities cannot cause characters’ STR to be lowered.” If such a plot were revealed, and a participating character was given a +2 STR using Iron Fleet Scout, that character’s STR would still go back to normal at the end of the challenge, rather than remaining at +2 indefinitely. In general, the game treats the expiration of an ability as something separate than the ability, which means a card that enters play due to the expiration of a lasting effect is not entering play using a card ability.