Cheapest priced copy (Dominaria): $0.99 at Card Kingdom, near mint, their price list as of .
Lich's Mastery 
Legendary Enchantment · Rare · Dominaria · #98
Hexproof
You can't lose the game.
Whenever you gain life, draw that many cards.
Whenever you lose life, for each 1 life you lost, exile a permanent you control or a card from your hand or graveyard.
When Lich's Mastery leaves the battlefield, you lose the game.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.99 to $6.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Dominaria | 98 | Rare | $0.99 | $2.49 |
| Dominaria Promos | 98s | Rare | — | $6.49 |
5 rulings from Wizards of the Coast
- 27 April 2018If you’re dealt more damage than you have cards to exile, you’ll just exile everything you can.
- 27 April 2018While you can’t lose the game, your opponents can still win the game if an effect says so.
- 27 April 2018You don’t have to exile all the cards from one place. For example, if a source deals 5 damage to you, you may exile one permanent, two cards from hand, and two cards from your graveyard.
- 27 April 2018If you run out of other permanents, cards in hand, and cards in graveyard, you’ll have to exile Lich’s Mastery itself and lose the game.
- 27 April 2018While you control Lich’s Mastery, your life total still changes. Lich’s Mastery’s effects don’t replace the life gain or life loss.