Nontoken creatures are enchantments in addition to their other types.
Constellation — Whenever an enchantment you control enters, you gain 1 life.
Whenever chaos ensues, choose a color. Add an amount of mana of that color equal to your devotion to that color.
(14/04/2023)
Nyx’s first ability will apply to nontoken creatures from the moment they enter the battlefield. Notably, a nontoken creature entering the battlefield will cause the constellation ability to trigger.
(14/04/2023)
A player’s devotion to a color is equal to the number of mana symbols of that color among the mana costs of permanents that player controls.
(14/04/2023)
The chaos ability isn’t a mana ability. It uses the stack and can be responded to. You choose the color as the ability resolves. Once the ability starts resolving and you’ve chosen a color, it’s too late for anyone to respond and change your devotion to any color.
