Cheapest priced copy (Amonkhet): $0.35 at Card Kingdom, near mint, their price list as of .
Merciless Javelineer 
Creature — Minotaur Warrior · 4/2 · Uncommon · Amonkhet · #202
{2}, Discard a card: Put a -1/-1 counter on target creature. That creature can't block this turn.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Amonkhet | 202 | Uncommon | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 18 April 2017The target creature won’t be able to block even if the -1/-1 counter is removed from it or if the -1/-1 counter can’t be put on it.
- 18 April 2017Once a creature has blocked, Merciless Javelineer’s ability can’t undo that block.