Cheapest priced copy (Commander Masters): $0.99 at Card Kingdom, near mint, their price list as of .
Demonlord Belzenlok 
Legendary Creature — Elder Demon · 6/6 · Mythic · Secret Lair Drop · #159
Flying, trample
When Demonlord Belzenlok enters, exile cards from the top of your library until you exile a nonland card, then put that card into your hand. If the card's mana value is 4 or greater, repeat this process. Demonlord Belzenlok deals 1 damage to you for each card put into your hand this way.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
6 printings · $0.99 to $2.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Masters | 151 | Rare | $0.99 | $1.49 |
| Commander Masters | 510 | Rare | — | — |
| Dominaria | 86 | Mythic | $0.99 | $1.99 |
| Dominaria Promos | 86s | Mythic | — | $2.49 |
| Secret Lair Drop | 159 | Mythic | $2.29 | $2.79 |
| Secret Lair Drop | 159★ | Mythic | — | — |
6 rulings from Wizards of the Coast
- 27 April 2018If the nonland card doesn't have a mana cost, its mana value is 0.
- 27 April 2018Demonlord Belzenlok's ability causes it to deal an amount of damage to you all at once; it doesn't deal 1 damage multiple times.
- 27 April 2018The mana value of a split card, such as a card with aftermath from the Amonkhet block, is equal to the combined mana cost of its two halves.
- 27 April 2018Land cards exiled this way remain exiled.
- 27 April 2018Once the triggered ability resolves, the ability will continue until you either exile a nonland card with mana value 3 or less or fail to exile any nonland cards while performing the process. You can't choose to stop receiving the blessings of Demonlord Belzenlok any sooner.
- 27 April 2018If the mana cost of the nonland card includes {X}, X is considered to be 0.