mtg cards like painter's servant choose a color DDR#42 - Painter's Servant +

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Since then, several of these unique creature types have been supplanted with other, more-appropriate or more-established creature types or been entirely removed in successive iterations of errata and the Grand Creature Type Update

The only way to become the monarch, other than dealing damage to an existing monarch, is to play any of the cards that state you become the monarch like Thorn of the Black Rose or Crown-Hunter Hireling

However, the site has some rules

When a sagas last ability goes on the stack, the saga actually sits in play until that ability resolves

They serve to give your side of the board tempo by allowing your creatures to attack (removing defenders), giving you more time to set up the board (removing attackers/expensive creatures), and allow for combat tricks (saving your creatures after damage is on the stack