Harrow still didn’t turn round, but Gideon knew innately that her eyes were rolling. “The Second House study contained a full and perfect explanation of the theorem which had been used to articulate the construct. Having studied that theorem, any halfway competent necromancer would be able to reproduce its effects. I now possess the competencies required to ride another living soul. I’m perhaps even more interested in what I’ve learned from the theorem behind the construct.”
“Making big shitty bone hunks.” Gideon preferred not to think about riding another living soul.
At that, Harrow had stopped—almost at the head of the staircase—and finally looked around. “Nav,” she’d said. “I could already make bone hunks. But now I can make them regenerate.”
The outcome literally nobody wanted.

Gideon the Ninth - Act Three, Chapter Twenty