Magar of the Magic Strings + Last Chance + Day's Undoing

Magar of the Magic Strings

Last Chance

Day's Undoing

How it works

1. Cast Last Chance by paying its mana cost, causing you to take an extra turn after this one and to lose the game at the beginning of that turn's end step.
2. Activate Magar by paying 1, noting Last Chance and putting it face down on the battlefield as a 3/3 creature.
3. Activate Magar by paying 1, noting Day's Undoing and putting it face down on the battlefield as a 3/3 creature.
4. During your next turn, deal combat damage to an opponent using the face down creatures that have Last Chance and Day's Undoing noted. The creatures trigger.
5. Resolve the first trigger, casting a copy of Last Chance without paying its mana cost. Resolve the copy, causing you to take an extra turn after this one and to lose the game at the beginning of that turn's end step.
6. Resolve the second trigger, casting a copy of Day's Undoing without paying its mana cost. Resolve the copy, causing you to end the turn. This will prevent the Last Chance trigger from causing you to lose the game.
7. Repeat from step 3.

This loop turns Magar of the Magic Strings into a devastating engine by smuggling dangerous sorceries directly into combat as 3/3 creatures. When those face-down attackers deal combat damage, they trigger to cast free copies of Last Chance for extra turns and Day's Undoing to reset your resources. The true brilliance lies in Day's Undoing's rules text: casting it during your turn immediately ends the turn, which neatly dodges the lethal delayed trigger that Last Chance would otherwise impose at the end step while letting you loop the sequence indefinitely.