Does Snapvine's Carnivorous ability deal combat damage or ability damage, and can Unyielding Spirit prevent it?

Ruling: Snapvine's Carnivorous ability instructs Snapvine and the target unit to deal damage to each other. This damage is neither ability damage nor combat damage, so Unyielding Spirit cannot prevent it and stun does not stop it.

Nuances:

• The same principle applies to Challenge and Last Breath abilities with similar wording
• Because it is not combat damage, stun does not prevent the damage