What spells and abilities does Unyielding Spirit not prevent?

Ruling: Unyielding Spirit does not prevent damage from Challenge, Snapvine, Gentlemen's Duel, Dragon's Rage, and Last Breath effects because these cards have units deal the damage rather than the spell or ability itself dealing the damage.

Nuances:

• The key distinction is whether the unit deals the damage versus the spell/ability dealing the damage directly