Cheapest priced copy (March of the Machine Commander): $0.39 at Card Kingdom, near mint, their price list as of .
Knights of the Black Rose 
Creature — Human Knight · 4/4 · Uncommon · March of the Machine Commander · #332
When this creature enters, you become the monarch.
Whenever an opponent becomes the monarch, if you were the monarch as the turn began, that player loses 2 life and you gain 2 life.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
3 printings · $0.39 to $5.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Conspiracy: Take the Crown | 76 | Uncommon | $0.59 | $5.99 |
| March of the Machine Commander | 332 | Uncommon | $0.39 | — |
| The List | MOC-332 | Uncommon | — | — |
5 rulings from Wizards of the Coast
- 23 August 2016Abilities that trigger whenever you “become the monarch” trigger only if you aren't already the monarch. For example, if you are already the monarch as Custodi Lich enters the battlefield, its last ability won't trigger.
- 23 August 2016If the triggered ability that causes the monarch to draw a card goes on the stack, and a different player becomes the monarch before that ability resolves, the first player will still draw the card.
- 23 August 2016The last ability of Knights of the Black Rose will trigger even if the most recent monarch was another player, as long as you were monarch as the turn began.
- 23 August 2016The game starts with no monarch. Once an effect makes one player the monarch, the game will have exactly one monarch from that point forward.
- 23 August 2016Being the monarch carries two inherent triggered abilities. “At the beginning of the monarch's end step, that player draws a card” and “Whenever a creature deals combat damage to the monarch, its controller becomes the monarch.”