When Knights of the Black Rose enters the battlefield, 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.
8/23/2016 The 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.
8/23/2016 The game starts with no monarch. Once an effect makes one player the monarch, the game will have exactly one monarch from that point forward.
8/23/2016 Abilities 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.
8/23/2016 If 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.