Cheapest priced copy (Phyrexia: All Will Be One): $0.49 at Card Kingdom, near mint, their price list as of .
Argentum Masticore 
Artifact Creature — Phyrexian Masticore · 5/5 · Rare · Phyrexia: All Will Be One Promos · #222p
First strike, protection from multicolored
At the beginning of your upkeep, sacrifice this creature unless you discard a card. When you discard a card this way, destroy target nonland permanent an opponent controls with mana value less than or equal to the mana value of the discarded card.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $0.49 to $0.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Phyrexia: All Will Be One | 222 | Rare | $0.49 | $0.49 |
| Phyrexia: All Will Be One | 393 | Rare | $0.59 | $0.79 |
| Phyrexia: All Will Be One Promos | 222p | Rare | $0.49 | $0.79 |
| Phyrexia: All Will Be One Promos | 222s | Rare | — | $0.69 |
2 rulings from Wizards of the Coast
- 4 February 2023Notably, this means that you may discard a card to keep Argentum Masticore on the battlefield even if there isn't a legal target for that second triggered ability. In that case, no players may respond to the second triggered ability and it does not resolve.
- 4 February 2023You don't choose a target for Argentum Masticore's upkeep triggered ability at the time it triggers. Rather, a second "reflexive" ability triggers when you discard a card this way. You choose a target for that ability as it goes on the stack. Each player may respond to this triggered ability as normal.