Jace, the Mind Sculptor
Legendary Planeswalker — Jace
+2: Look at the top card of target player's library. You may put that card on the bottom of that player's library.
0: Draw three cards, then put two cards from your hand on top of your library in any order.
−1: Return target creature to its owner's hand.
−12: Exile all cards from target player's library, then that player shuffles their hand into their library.
Illustrated by
From the Vault: Twenty#18MythicEnglishLegality
Rulings
You draw three cards and put two cards back all while Jace’s second ability is resolving. Nothing can happen between the two, and no player may choose to take actions.
If the targeted player for Jace’s last ability has no cards in hand, that player shuffles nothing into their library, and that player’s library will remain empty. That player won’t lose the game until they try to draw from the empty library.