Primordial Roar

Primordial Roar and Show Off

What happens when the unit on the board that I Showed Off with Primordial Roar is returned to my hand with Star-Crossed? Do I still deal damage? What about if I play Lunar Boon and discard the unit from hand?

You still deal damage in both scenarios.

Any referenced characteristics of shown off objects are locked in when you show them off. Regardless of what subsequently happens to them, their information will be able to be checked by the card that showed them off. This also means that giving a unit +[M] or -[M] after showing that unit off will not affect the damage dealt by Primordial Roar; it's too late by that point.

Relevant rules: 832.1.d.1.

832.1.d. Linked abilities and instructions can reference information about the shown off object/s. Example: Primordial Roar is a spell that reads "[Show Off] a unit," and "If you showed off a unit, deal damage equal to that unit's Might to a unit."

832.1.d.1. The information referenced in this way is checked when the card/s in question are shown off during finalization. Any later changes to the shown off objects will not be considered. Example: Primordial Roar is played showing off a friendly unit with 4 [M] and an enemy unit with 3 [M]. In reaction to Primordial Roar, an opponent plays Frigid Touch, giving the friendly unit -2 [M] this turn. Because the information was checked when the friendly unit was shown off, the spell still deals 4 damage to the enemy unit, killing it.