Flying
Whenever a player attacks one of your opponents, if that opponent has more life than another of your opponents, that attacking player draws a card and you put two +1/+1 counters on a creature you control.
Breena’s triggered ability will trigger even if you control no creatures.
If the attacking player is one of your opponents and has less life than the player being attacked, then the condition is satisfied.
You choose which creature to put +1/+1 counters on as the ability is resolving. Once you make the choice, no player may take actions until the counters are placed.