Cheapest priced copy (Iconic Masters): $0.59 at Card Kingdom, near mint, their price list as of .
Malfegor 
Legendary Creature — Demon Dragon · 6/6 · Mythic · Commander Anthology · #184
Flying
When Malfegor enters, discard your hand. Each opponent sacrifices a creature of their choice for each card discarded this way.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
5 printings · $0.59 to $9.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Anthology | 184 | Mythic | $0.99 | — |
| Commander 2011 | 208 | Mythic | $0.99 | — |
| Conflux | 117 | Mythic | $1.49 | $9.99 |
| Iconic Masters | 205 | Rare | $0.59 | $1.49 |
| Conflux Promos | 117★ | Mythic | — | $0.99 |
2 rulings from Wizards of the Coast
- 17 November 2017After you discard your hand and the number of creatures each opponent must sacrifice has been determined, each opponent in turn order, starting with the player whose turn it is if that player is your opponent, chooses which creatures they will sacrifice, then all the chosen creatures are all sacrificed at the same time.
- 17 November 2017Malfegor’s ability is not optional. You must discard your entire hand no matter how many creatures your opponents control.