If multiple effects modify how damage will be dealt, the player who would be dealt damage chooses the order to apply the effects. For example, say you’ve activated Vengeful Archon’s ability with X = 3 targeting Player A, and you’ve activated Vengeful Archon’s ability with X = 1 targeting Player B. You’re dealt 2 damage. You can apply the first prevention effect (dealing 2 damage to Player A), or you can apply the second prevention effect (dealing 1 damage to Player B) followed by the first prevention effect (dealing 1 damage to Player A). The unused portions of the prevention effects remain.