Cheapest priced copy (The Brothers' War Commander): $1.99 at Card Kingdom, near mint, their price list as of .
Unbreakable Formation 
Instant · Rare · Ravnica Allegiance · #29
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.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
16 printings · $1.99 to $27.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| The Brothers' War Commander | 78 | Rare | $1.99 | — |
| Commander Legends: Battle for Baldur's Gate | 710 | Rare | $2.49 | — |
| Commander Legends | 388 | Rare | $2.29 | — |
| Dominaria United Commander | 106 | Rare | $2.29 | — |
| Tales of Middle-earth Commander | 179 | Rare | $2.29 | — |
| Midnight Hunt Commander | 95 | Rare | $2.29 | — |
| March of the Machine Commander | 213 | Rare | $2.29 | — |
| Ravnica Allegiance Promos | 29p | Rare | $3.99 | $3.49 |
| Ravnica Allegiance Promos | 29s | Rare | — | $2.99 |
| URL/Convention Promos | 2025-5 | Rare | — | $27.99 |
| Ravnica Allegiance | 29 | Rare | $2.49 | $2.99 |
| Ravnica Remastered | 32 | Rare | $1.99 | $2.49 |
| Secret Lair Countdown | 56 | Rare | — | — |
| Secret Lair Drop | 310 | Rare | $3.99Out of stock | $2.99Out of stock |
| Secret Lair Drop | 2827 | Rare | — | — |
| Secret Lair Drop | 7052 | Rare | $2.99 | $3.49 |
3 rulings from Wizards of the Coast
- 25 January 2019Unbreakable 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 January 2024If 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.
- 12 January 2024Addendum 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.