Battalion — Whenever Ordruun Veteran and at least two other creatures attack, Ordruun Veteran gains double strike until end of turn. (It deals both first-strike and regular combat damage.)
Once a battalion ability has triggered, it doesn’t matter how many creatures are still attacking when that ability resolves.
The effects of battalion abilities vary from card to card. Read each card carefully.
The three attacking creatures don’t have to be attacking the same player or planeswalker.