Vengeful Archon

The effect of Vengeful Archon’s ability is not a redirection effect. If it prevents damage, Vengeful Archon (not the source of that damage) deals damage to the targeted player as part of that prevention effect. Vengeful Archon is the source of the new damage, so the characteristics of the original source (such as its color, or whether it had lifelink or deathtouch) don’t affect this damage. The new damage is not combat damage, even if the prevented damage was.

If Vengeful Archon’s ability prevents damage, Vengeful Archon deals its damage immediately afterward as part of that same prevention effect. This happens before state-based actions are checked, and before any player can cast spells or activate abilities. If a spell or ability would have caused that damage to be dealt, this happens before that spell or ability resumes its resolution.

If you would be dealt combat damage by multiple attacking creatures, you choose which of that damage to prevent. For example, if X is 3 and you’d be dealt combat damage by a 1/3 Scroll Thief and a 3/5 Siege Mastodon, you might choose to prevent 1 damage from the Scroll Thief and 2 damage from the Siege Mastodon. You don’t decide until the point at which the creatures would deal their damage.