Snake Umbra

Snake Umbra grants the triggered ability to the creature. It triggers whenever the enchanted creature deals damage to an opponent of its controller (who is not necessarily an opponent of the Aura's controller). In other words, if your Snake Umbra winds up enchanting your opponent's creature, that opponent will draw a card whenever that creature damages you.

The ability triggers when the enchanted creature deals any damage, not just combat damage.

If a spell or ability says that it would "destroy" a creature enchanted with an Aura that has umbra armor, that spell or ability is what causes the Aura to be destroyed instead. Umbra armor doesn't destroy the Aura; rather, it changes the effects of the spell or ability. On the other hand, if a spell or ability deals lethal damage to a creature enchanted with an Aura that has umbra armor, the game rules regarding lethal damage cause the Aura to be destroyed, not that spell or ability.