Dominaria Spoiler Digest - Who's Who and What's What from the Release Notes
Marchesa, the Black Rose
Dethrone (Whenever this creature attacks the player with the most life or tied for most life, put a +1/+1 counter on it.)
Other creatures you control have dethrone.
Whenever a creature you control with a +1/+1 counter on it dies, return that card to the battlefield under your control at the beginning of the next end step.
5/29/2014 If a creature has multiple instances of dethrone, each triggers separately.
5/29/2014 If the creature card leaves the graveyard before the delayed triggered ability resolves, that card won’t return to the battlefield, even if it’s back in the graveyard when the delayed triggered ability resolves.
5/29/2014 If Marchesa has a +1/+1 counter on it when it dies, it will return to the battlefield under your control because of its own ability.
5/29/2014 Dethrone doesn’t trigger if the creature attacks a planeswalker, even if its controller has the most life.
5/29/2014 Once dethrone triggers, it doesn’t matter what happens to the players’ life totals before the ability resolves. You’ll put a +1/+1 counter on the creature even if the defending player doesn’t have the most life as the ability resolves.
5/29/2014 The +1/+1 counter is put on the creature before blockers are declared.
5/29/2014 In a Two-Headed Giant game, dethrone will trigger if the creature attacks the team with the most life or tied for the most life.