Whenever you cast an instant or sorcery spell, Spellrune Painter gets +1/+1 until end of turn.

Daybound (If a player casts no spells during their own turn, it becomes night next turn.)

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Spellrune Howler

Whenever you cast an instant or sorcery spell, Spellrune Howler gets +2/+2 until end of turn.

Nightbound (If a player casts at least two spells during their own turn, it becomes day next turn.)

Whenever you cast an instant or sorcery spell, this creature gets +1/+1 until end of turn.
Daybound (If a player casts no spells during their own turn, it becomes night next turn.)

Whenever you cast an instant or sorcery spell, this creature gets +2/+2 until end of turn.
Nightbound (If a player casts at least two spells during their own turn, it becomes day next turn.)