Cheapest priced copy (Ixalan): $0.35 at Card Kingdom, near mint, their price list as of .
Steadfast Armasaur 
Creature — Dinosaur · 2/3 · Uncommon · Ixalan · #39
Vigilance
{1}{W}, {T}: This creature deals damage equal to its toughness to target creature blocking or blocked by it.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Ixalan | 39 | Uncommon | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 29 September 2017Tapping an attacking or blocking creature doesn't remove it from combat. If the target of Steadfast Armasaur's ability survives the damage, Steadfast Armasaur will deal combat damage to and be dealt combat damage by that creature as normal.
- 29 September 2017If Steadfast Armasaur is no longer on the battlefield as its ability resolves, use its toughness as it last existed on the battlefield to determine how damage is dealt.