Orim's Thunder

Kicker {R} (You may pay an additional {R} as you cast this spell.)
Destroy target artifact or enchantment. If this spell was kicked, it deals damage equal to that permanent's mana value to target creature.

Dominaria Remastered

Commander Anthology Volume II

Kicker {R} (You may pay an additional {R} as you cast this spell.)
Destroy target artifact or enchantment. If this spell was kicked, it deals damage equal to that permanent's converted mana cost to target creature.

Commander Anthology

Kicker {R} (You may pay an additional {R} as you cast this spell.)
Destroy target artifact or enchantment. If Orim's Thunder was kicked, it deals damage equal to that permanent's converted mana cost to target creature.

Commander 2015

Commander 2011

If Orim's Thunder is kicked, but the artifact or enchantment is an illegal target as Orim's Thunder tries to resolve, Orim's Thunder won't be able to determine the artifact or enchantment's mana value. No damage will be dealt to the target creature, even if it remained a legal target. If only the creature has become an illegal target, the artifact or enchantment will still be destroyed. (If both targets become illegal, Orim's Thunder won't resolve at all.)

If Orim's Thunder is kicked, it's the source of damage dealt to the target creature, not the artifact or enchantment.