In a nutshell:
- Ending the turn does exactly that. The specific procedure the game uses to end the turn consists of these steps:
- Any triggered abilities that have triggered, but not been put on the stack yet cease to exist.
- Exile every object on the stack and remove all creatures and planeswalkers from combat.
- Check state based actions.
- The current phase or step ends, and the game proceeds directly to the cleanup step (any steps/phases between the current one and the cleanup step are skipped).
Q: Nicole plays Time Stop during Amy’s upkeep. During Amy’s next upkeep, Nicole wants to flash Time Stop back with Torrential Gearhulk. Can she?
A: Not unless Time Stop was countered. One step in ending the turn is to exile all spells and abilities on the stack. This includes Time Stop, even though it is in the process of resolving as this instruction happens. Fortunately, there is a special rule that states that once it starts, the resolution of Time Stop will continue to completion even though the card isn’t on the stack anymore.
Q: Amy plays Supreme Verdict, then Nicole responds with Time Stop. What happens?
A: As part of ending the turn, all spells and abilities on the stack are exiled. This is a distinct game action from countering, so Supreme Verdict’s “can’t be countered” does nothing to prevent this.
Q: Amy uses Kiki-Jiki, Mirror Breaker to make a copy of her Serra Angel and attacks with the token. During her second main phase, Amy activates Sundial of the Infinite. What happens to the token?
A: Kiki-Jiki’s ability stipulates that the token is sacrificed during the next end of turn step. Ending the turn makes the game jump straight to the cleanup step, skipping any steps in between. Because the end of turn step is skipped on Amy’s turn, the ability that makes Amy sacrifice the token will not trigger until the following end of turn step on Nicole’s turn.
Note: If Amy was a bit more savvy, she would have waited until the sacrifice trigger happened during her end step and activated Sundial of the Infinite in response. The sacrifice trigger would be exiled in the process of ending the turn, but since it triggered already, it won’t trigger during any future end steps, allowing Amy to keep the token indefinitely.
Q: Amy casts Final Fortune and activates Sundial of the Infinite during the second main phase of her extra turn. What happens?
A: Like in the previous question, ending the turn advances the game directly to the cleanup step, which means that the “you lose the game” trigger doesn’t happen, since the step it was going to trigger in gets skipped. Unlike the previous question, Final Fortune specifies that it triggers at the beginning of “that turn’s” end step only, which means that it will never happen during any subsequent end steps either.
Q: Amy casts Day’s Undoing while she controls Sphinx’s Tutelage. What happens?
A: Amy drawing cards for Day’s Undoing causes Sphinx’s Tutelage to trigger 7 times. These triggers are not put onto the stack immediately, though; normally, the game would do that the next time a player would get priority. In this case, though, because the turn ends, these triggers never make it onto the stack. The first step in the process of ending the turn is to kill all such triggered abilities that have triggered but aren’t on the stack yet.
Note: Triggered abilities that trigger during the process of ending the turn still happen. The rule cited above only preempts triggered abilities that trigger before the action of ending the turn starts.