His attacks do not have to hit a hero in order to trigger this ability - therefore the only way to stop him summoning a minion in a turn is either to stun him, or for there to be 3 of them existing already. Each time he uses an attack, he creates a skeleton enemy in rank 1, steadily pushing himself back until he is in position 4, where his attacks no longer spawn anything. The Necromancer will always start in position 1.

Freed from the trappings of their humanity, they plied their terrible trade anew: the dead reviving the dead, on and on, down the years.

I brought my colleagues back with much of their intellect intact - a remarkable triumph for even the most experienced necromancer. Having learned all I could from my visiting guests, I murdered them as they slept. I entertained a delegation of experts from overseas, eager to plumb the depths of their knowledge and share with them certain techniques and alchemical processes I had found to yield wondrous and terrifying results.

Who could have divined the prophetic import of something as unremarkable. I began in humility, but my ambition was limitless. Mastery over life and death was chief among my early pursuits.

Hag team darkest dungeon