One of my favorite Dark Knight/Shadowknight abilities was from a game on the PS2 call Champions: Return to Arms, it was a console version of Everquest.
Shadowknights got an ability called Raise Army which would bring back the enemies you killed and they would chase down and attack any mobs on the screen.

They weren't as strong after bringing them back from the dead and they would die quickly to bosses, but it was still a great and fun ability to watch them swarm everything. Once you got the ability powered up you could have like 20 of them all following you around ready to jump on the next mob you encounter.