When playing Last Breath on Yasuo readied from Base, does he deal damage twice (8 total) or once (4), and does he die this round? Also, when a card returns from battlefield to Base, is it ready or exhausted?

Ruling: Last Breath only readies a unit and has it deal its might as damage to another unit at a battlefield. Nothing else happens as a result of this spell - if you later attack with Yasuo, that's unrelated to Last Breath.

Nuances:

• Move abilities do not modify the exhausted state unless they explicitly say so
• If a card was exhausted when moved, it stays exhausted; if ready, it stays ready