Does Bellows Breath repeated deal 2 instances of 2 damage or 4 damage simultaneously?

Bellows Breath with Repeat does not deal 4 damage simultaneously, nor does it deal 2 damage per instance.

When you pay the Repeat cost for Bellows Breath, it executes its effect—"Deal 1 to up to three units at the same location"—a second time. This results in two separate instances of 1 damage being dealt, not 2 damage at once.

Here is the breakdown of how this works:

1. Two Separate Instances: The spell resolves its first instance (dealing 1 damage to up to three chosen units), and then resolves its second instance (dealing 1 damage to up to three chosen units).
2. Not Simultaneous: These two instances are distinct. While they occur during the resolution of the same spell (meaning no cleanup or reactions happen between them), they are not a single "4 damage" event.
3. Targeting: Because each instance is separate, you can choose different targets for the second instance, and you can even choose a different location for the second instance (as confirmed by the FAQ).
4. Damage Marking: Each instance of 1 damage is marked on the units separately. If you target the same unit with both instances, it will have 2 damage marked on it by the time the spell finishes resolving.

According to Rule 746.1.d, Repeat is functionally short for executing the instructions of the spell one additional time. Since the instruction is "Deal 1 to up to three units," the spell performs that specific action twice.