Cheapest priced copy (Commander 2018): $0.49 at Card Kingdom, near mint, their price list as of .
Magus of the Balance 
Creature — Human Wizard · 2/2 · Rare · Commander 2018 · #5
{4}{W}, {T}, Sacrifice this creature: Each player chooses a number of lands they control equal to the number of lands controlled by the player who controls the fewest, then sacrifices the rest. Players discard cards and sacrifice creatures the same way.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2018 | 5 | Rare | $0.49 | — |
| Commander Legends: Battle for Baldur's Gate | 699 | Rare | $0.49 | — |
3 rulings from Wizards of the Coast
- 13 July 2018Players can't take actions once Magus of the Balance's ability begins to resolve until it's done resolving. If any abilities trigger during this process, they're put onto the stack after it's done resolving.
- 13 July 2018When Magus of the Balance's ability resolves, first the player whose turn it is chooses an appropriate number of lands they control (which may be zero if that player doesn't control more lands than the player who controls the fewest). Then each other player in turn order does the same, knowing choices made by previous players. Finally, all of the chosen lands are sacrificed simultaneously. Players repeat this process for cards in hand and creatures they control, except while choosing cards in hand, players won't know the identity of cards chosen by the previous players.
- 13 July 2018If a player has zero cards in hand, controls no lands, or controls no creatures, other players will have to discard their entire hand, sacrifice all of their lands, or sacrifice all of their creatures, as appropriate.