If a targeted spell's target becomes invalid after the spell is on the chain (e.g., removed by Retreat), does the spell fizzle or does the caster choose a new target?

Ruling: The spell does nothing (whiffs). Targets cannot be redeclared after an effect has been placed onto the chain.

Sequence:

• Super Mega Death Rocket is played targeting the 5 Might Unit
• Retreat is played in reaction
• Chain resolves backwards: Retreat removes the targeted unit
• Super Mega Death Rocket resolves with an invalid target and does nothing

Nuances:

• The spell does not retarget to another valid unit (like the Jinx player's own unit)