If my opponent plays Icathian Rain and kills my Tasty Faefolk (which has a hidden Zhonya's at the battlefield), can I activate the hidden Zhonya's in response to the Faefolk's deathknell trigger to save the Zhonya's (have it recall to base) without saving the Faefolk?

Ruling: Whether you can save the hidden Zhonya's by playing it in response to Faefolk's deathknell depends on whether the death occurs during combat or outside of combat. Outside of combat (in the action phase), you lose control of the battlefield immediately when Faefolk dies, so the hidden Zhonya's goes to trash before you can play it. During combat, you maintain control of the battlefield until contested is cleared, so you can play the hidden Zhonya's in response to the deathknell and it will recall to base.

Sequence:

• Outside combat: Faefolk dies → you lose battlefield control → hidden Zhonya's goes to trash
• During combat: Faefolk dies → deathknell triggers → you still control battlefield (contested not yet cleared) → you can play hidden Zhonya's → Zhonya's recalls to base

Nuances:

• Playing Zhonya's after the deathknell trigger cannot save the Faefolk because Zhonya's cannot look back at deaths that happened before it was played
• The combat timing interaction is based on current rules as written but is acknowledged as unclear/problematic and may be changed in future rules updates
• If Faefolk dies specifically during combat damage (not during combat showdown from an action/reaction), the interaction is currently unclear
• Playing a unit (not just gear) in response to a deathknell during this window would break the game and requires judge intervention