2012-06-01
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.
2012-06-01
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.