Boros Elite

Oracle Text

Battalion — Whenever Boros Elite and at least two other creatures attack, Boros Elite gets +2/+2 until end of turn.

Card Rulings

4/15/2013 The three attacking creatures don't have to be attacking the same player or planeswalker.
4/15/2013 Once a battalion ability has triggered, it doesn't matter how many creatures are still attacking when that ability resolves.
4/15/2013 The effects of battalion abilities vary from card to card. Read each card carefully.