Cheapest priced copy (Adventures in the Forgotten Realms Promos): $12.99 at Card Kingdom, near mint, their price list as of .
The Book of Exalted Deeds 
Legendary Artifact — Book · Mythic · Adventures in the Forgotten Realms · #4
At the beginning of your end step, if you gained 3 or more life this turn, create a 3/3 white Angel creature token with flying.
{W}{W}{W}, {T}, Exile The Book of Exalted Deeds: Put an enlightened counter on target Angel. It gains "You can't lose the game and your opponents can't win the game." Activate only as a sorcery.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
6 printings · $12.99 to $54.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Adventures in the Forgotten Realms | 4 | Mythic | $13.99 | $14.99 |
| Adventures in the Forgotten Realms | 359 | Mythic | $14.99 | $17.99 |
| Adventures in the Forgotten Realms Promos | 4a | Mythic | — | $54.99Out of stock |
| Adventures in the Forgotten Realms Promos | 4p | Mythic | $12.99 | $14.99 |
| Adventures in the Forgotten Realms Promos | 4s | Mythic | — | $22.99 |
| The List | AFR-4 | Mythic | $13.99 | — |
2 rulings from Wizards of the Coast
- 23 July 2021The Angel won't lose the ability it gains if it stops being an Angel after the ability resolves.
- 23 July 2021The enlightenment counter placed by the last ability serves as a memory aid. It isn't connected to the granted ability. The Angel keeps that ability even if it loses the counter. Similarly, if the counter is somehow moved to another permanent, that permanent doesn't gain the ability.