Does Soul-Scar Mage convert non-combat damage from enchantments into -1/-1 counters?

Soul-Scar Mage reads: 'If a spell you control would deal damage to a creature, it deals that much damage in the form of -1/-1 counters instead.' The key word is spell. Enchantments, once on the battlefield, are permanents, not spells (CR 111.1).

A 'spell' is a card on the stack (CR 111.1). Once an enchantment resolves and enters the battlefield, it is no longer a spell — it is a permanent. Any damage it deals afterward does not qualify for Soul-Scar Mage's replacement effect (CR 614.1).

So if you control Soul-Scar Mage and a Pestilence Demon, and Pestilence Demon's activated ability deals damage to creatures, that damage is NOT converted to -1/-1 counters. Likewise, an enchantment like Powerstone Shard dealing damage would not be converted.

Example: You control Soul-Scar Mage and enchant a creature with Captive Flame, which deals 1 damage each upkeep. That 1 damage is dealt by a permanent (the enchantment), not a spell, so it remains regular damage and does not become a -1/-1 counter.

The effect does apply to instants and sorceries you cast, as those are spells on the stack when they deal damage. For example, a Lightning Bolt you cast would deal its 3 damage as three -1/-1 counters on the target creature (CR 119.3).