When you take the merciless node in Bone curse you can no longer curse enemies, only minions.
Based on the wording “You MAY cast bone curse on your minions” i believe it is working incorrectly, if you take merciless, when you cast bone curse it should affect all enemies and allied minions in the area.
If this is intended and it is currently working correctly, I would recommend changing it to affecting all minions + enemies as currently it has anti-synergy with entreat the damned (summon a vanguard skele, except you cant cast it on an enemy in order to summon one) plus you have a lot of dead skill points as you dont want to make your bone curse worse for your minions after youve taken 9 of so points in the minion buff nodes.