I think should have 3 specs, and I think all of them should summon lots of minions for a small amount of time. And all the three specs should consume corpses of summoned minions too fulfill his role, except for both dps that should keep as much summoned minions while consuming them to have better dps (minions also deal damage).
Ranged caster dps and support: consume a minion to buff the party and his minions, explode a minion to disease and dot the enemy or/and CC de enemy.
Tank and support: consume a minion to heal himself, consume a minion to buff the party and his minions, and explode a minion to threat or taunt the enemy, consume a minion to create an armor with his bones for damage reduction.
Melee dps and support: consume a minion to buff the party and his minions, consume a minion to imbue the weapon with dark magic for the next hit (dealing more damage and elemental damage).