Cheapest priced copy (The List): $0.35 at Card Kingdom, near mint, their price list as of .
Angelic Exaltation 
Enchantment · Uncommon · Ravnica Allegiance · #2
Whenever a creature you control attacks alone, it gets +X/+X until end of turn, where X is the number of creatures you control.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $0.35 to $0.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| The List | RNA-2 | Uncommon | $0.35 | — |
| Ravnica Allegiance | 2 | Uncommon | $0.35 | $0.99 |
| Ravnica Remastered | 2 | Uncommon | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 25 January 2019The value of X is determined only as Angelic Exaltation’s ability begins to resolve. It won’t change later in the turn if the number of creatures you control changes.
- 25 January 2019A creature attacks alone if it’s the only creature declared as an attacker during the declare attackers step (including creatures controlled by your teammates, if applicable). For example, Angelic Exaltation’s ability won’t trigger if you attack with multiple creatures and all but one of them are removed from combat.