Am I allowed to cast 2 Falling Star spells to stack damage on a single unit at the enemy base?

Yes, you are allowed to cast two Falling Star spells to stack damage on a single unit at the enemy base.

How it works:

1. Targeting: Each Falling Star is an independent spell. When you play the first one, you declare its targets (you can choose the same unit for both instances of damage). When you play the second one, you declare its targets again (you can choose that same unit for both instances of damage).
2. Stacking: Because each spell resolves independently, the damage from the first spell and the damage from the second spell will both be applied to the unit.
3. Legality: There is no rule in Riftbound that prevents you from targeting the same unit with multiple instances of the same spell or multiple copies of the same spell.

Important Timing Note:

• Main Phase: You must play these spells during your Main Phase while you have Focus (an Open State).
• Chain Resolution: If you play the first Falling Star, it goes on the chain. You must allow players to pass priority (or play reactions) until the chain is empty and the first spell resolves. Once the chain is empty again, you regain Focus and can play the second Falling Star. You cannot play both spells at the exact same time; they must be played and resolved sequentially.

According to RiftJudge FAQ #8503, you are explicitly allowed to target the same unit with both instances of damage from a single Falling Star. Extending this logic to multiple spells, you can indeed stack the damage from two separate Falling Star casts onto one unit.