Indrik Umbra

Indrik Umbra does not give any creature the ability to block the enchanted creature. It just forces those creatures which are already able to block that creature to do so.

If, during a player's declare blockers step, a creature is tapped or it's affected by a spell or ability that says it can't block, then it doesn't block. If there's a cost associated with having a creature block, its controller isn't forced to pay that cost. The creature doesn't have to block.

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.