If Kha'Zix, Evolving Hunter attacks Diana, Lunari and Tactical Retreat is on top of the deck, can Diana's player draw and play it before Kha'Zix's ability kills Diana?

Ruling: No. When the showdown begins, both Diana's "When a showdown begins here" trigger and Kha'Zix's "When I attack" trigger go on the chain. Diana's trigger is placed on the chain first (bottom), and Kha'Zix's trigger is placed second (top). Because chains resolve in Last-In, First-Out (LIFO) order, Kha'Zix's trigger resolves first, dealing damage and killing Diana before her trigger resolves to draw the Tactical Retreat.

Sequence:

• Showdown begins, triggering Diana's ability
• Attacker/defender designations are established, triggering Kha'Zix's ability
• Diana's trigger goes on chain first (bottom)
• Kha'Zix's trigger goes on chain second (top)
• Kha'Zix's trigger resolves first, dealing lethal damage
• Diana's trigger resolves after she is already killed