If opponent plays Icathian Rain and I respond with Hidden Blade using Sett's ability to save my unit and bring it back to base, does Icathian Rain fizzle or still persist?

Ruling: Icathian Rain persists and does not fizzle. The IR triggers don't require the unit to be at a battlefield, and Sett's replacement effect keeps the unit on the board (just at base), so the triggers will still have a valid target and continue to resolve.

Sequence:

• Icathian Rain resolves and creates six reflexive triggers targeting units
• If you play Hidden Blade after IR triggers target, you can kill your buffed unit at various points in the sequence
• When the unit would die, Sett's replacement effect can prevent it from leaving the board by recalling it to base
• The remaining IR triggers still see the unit as a legal target at base and continue dealing damage to it
• If the unit was saved by Sett from the first death, the remaining triggers will kill it again

Nuances:

• If the buffed unit is exactly 7 Might with the buff, you must choose between drawing 2 from Hidden Blade or saving the unit - you cannot do both (the unit will be recalled at 6 Might after the buff is spent and then take 6 more damage from remaining triggers)
• If the unit is 7 Might or higher without the buff, you can both draw 2 and save it with Sett
• If the unit is 6 Might or less, Icathian Rain can kill it regardless of timing
• You can kill your buffed unit before IR resolves and decline Sett replacement to redirect all IR triggers to opponent's units (if you only control the buffed unit)