Cheapest priced copy (Rivals of Ixalan): $0.35 at Card Kingdom, near mint, their price list as of .
Stampeding Horncrest 
Creature — Dinosaur · 4/4 · Common · Rivals of Ixalan · #116
This creature has haste as long as you control another Dinosaur.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Rivals of Ixalan | 116 | Common | $0.35 | $0.49 |
One ruling from Wizards of the Coast
- 19 January 2018If it’s the turn Stampeding Horncrest comes under your control, and it loses haste after being declared as an attacker, it will continue to attack. It won’t be removed from combat. On the other hand, if it loses haste before your declare attackers step, it won’t be able to attack.