Cheapest priced copy (Hour of Devastation): $10.99 at Card Kingdom, near mint, their price list as of .
Crested Sunmare 
Creature — Horse · 5/5 · Mythic · The List · #HOU-6
Other Horses you control have indestructible.
At the beginning of each end step, if you gained life this turn, create a 5/5 white Horse creature token.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $10.99 to $24.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Hour of Devastation | 6 | Mythic | $10.99 | $24.99 |
| Hour of Devastation Promos | 6s | Mythic | — | $23.99 |
| The List | HOU-6 | Mythic | $10.99 | — |
| Secret Lair Drop | 1228 | Mythic | $20.99 | $20.99 |
3 rulings from Wizards of the Coast
- 14 July 2017Crested Sunmare’s triggered ability won’t trigger unless you’ve gained life in the turn before the end step began. It can’t be satisfied by another triggered ability causing you to gain life during that end step.
- 14 July 2017Crested Sunmare’s triggered ability cares only whether you gained life in the turn, even if Crested Sunmare wasn’t on the battlefield when that happened. It doesn’t care how much you gained, whether you also lost life, or even whether you lost more life than you gained.
- 14 July 2017If a creature has been dealt damage, that damage remains marked on it until the cleanup step. If another Horse you control has been dealt lethal damage, and later in the turn Crested Sunmare leaves the battlefield, that Horse will be destroyed.