Cheapest priced copy (Masters 25): $0.35 at Card Kingdom, near mint, their price list as of .
Coralhelm Guide 
Creature — Merfolk Scout Ally · 2/1 · Common · Battle for Zendikar · #74
{4}{U}: Target creature can't be blocked this turn.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
4 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Masters 25 | 49 | Common | $0.35 | $0.49 |
| Battlebond | 116 | Common | $0.35 | $0.49 |
| Battle for Zendikar | 74 | Common | $0.35 | $0.49 |
| The List | BBD-116 | Common | $0.35 | — |
One ruling from Wizards of the Coast
- 16 March 2018Activating Coralhelm Guide's ability after a creature has become blocked won't cause that creature to become unblocked.