When playing against Icathian Rain with a hidden unit card, when must the hidden unit be revealed, and can it be targeted by Icathian Rain's damage?

Ruling: You can wait until after Icathian Rain's 6 damage triggers are placed on the chain and targets are chosen before revealing your hidden unit. The hidden unit cannot be targeted by Icathian Rain if you don't reveal it before the targets are locked in.

Sequence:

• Opponent plays Icathian Rain
• You get priority and pass
• 6 triggers go on the stack, opponent must choose targets from only the valid (revealed) units
• You get priority again and can now play your hidden unit (and other reactions like Retreat)
• The targets have already been chosen, so your hidden unit is safe from Icathian Rain

Nuances:

• Icathian Rain itself does not deal damage directly; it creates 6 reflexive triggers that each require a chosen valid target as they go on the chain
• Only revealed units are valid targets when the triggers are placed on the chain