2015-06-22 : If multiple attacking creatures must be blocked if able, the defending player must assign at least one blocker to each of them if possible. For example, if two such creatures were attacking and there were two potential blockers, they couldn’t both be assigned to block the same attacker.

2015-06-22 : Joraga Invocation doesn’t force any specific creature to block any specific attacking creature. The defending player still chooses how creatures they control block.