Creatures you control gain indestructible until end of turn.
Addendum — If you cast this spell during your main phase, put a +1/+1 counter on each of those creatures and they gain vigilance until end of turn.
(25/01/2019)
Unbreakable Formation affects only creatures you control at the time it resolves. Creatures you begin to control later in the turn won't gain indestructible or vigilance and they won't get a +1/+1 counter.
(12/01/2024)
Addendum abilities of instant spells apply while the spell is resolving, not immediately after casting it. If the spell is countered, you don't get the addendum bonus.
(12/01/2024)
If an effect copies a spell with an addendum ability while it's on the stack, the copy wasn't cast at all, so you won't get the addendum bonus.
