Reckless Stormseeker // Storm-Charged Slasher

Before a player untaps their permanents during the untap step, the game checks to see if the day/night designation should change.

If you cast a spell with daybound during night, that spell will be front face up (that is, daybound face up) on the stack. However, it will enter the battlefield with its back face up (that is, with its nightbound face up). It won't enter with its daybound face up and then transform.

Double-faced permanents with daybound transform to their nightbound faces as it becomes night. Similarly, double-faced permanents with nightbound transform to their daybound faces as it becomes day. This happens immediately and is not a state-based action. It happens any time it becomes day or night, not just during the untap step.

If it is day, and the active player of the previous turn cast no spells during their turn, it becomes night.

If it is night, permanents with daybound that enter the battlefield without being cast will enter with their nightbound faces up.