Equipped creature gets +3/+1 and must be blocked by an Eldrazi if able.
7/13/2016 Only one Eldrazi is required to block the equipped creature. Other Eldrazi and non-Eldrazi creatures may also block that creature, and are free to block other creatures or not block at all.
7/13/2016 The defending player, not the attacking player, chooses which Eldrazi blocks the equipped creature.
7/13/2016 If each Eldrazi that could block the equipped creature is tapped or is affected by a spell or ability that says it can’t block, then none of them block. If there’s a cost associated with having each of those creatures block, its controller isn’t forced to pay the cost, so they don’t have to block in that case either.
7/13/2016 One creature equipped with multiple Slayer’s Cleavers only requires a single Eldrazi to block it.