Just keep beating him. There is a fixed 10% chance of true death, and you should get it done in 7-15 tries depending on RNG and your luck :)
Thanks!
I think I'm very unlucky (Note that this isn't my first session of trying to beat him)
That’s an impressive number of Scrolls of Resurrection :)
And after that I forgot to save, so I am at the start of the day again (Now I have to beat him again or at least try to)
Its done again
