ToME: the Tales of Maj'Eyal

The second necrosis talent as a passive ability is a source of unpredictable outgoing damage outside of the players control, it can fail pacifist missions in the infinite dungeon, slave rescue attempts and doubtless cause other issues when you are trying not kill everything around you for whatever reason you might have.
Making it a sustain without a resource cost that can't be dispelled would be ideal solution from my perspective. I would also be okay with it being able to be dispelled in exchange for the extra level of control.

In fact it might be a much better idea to roll this and spikes of decrepitude together, so that Across the veil is the sustain, and spikes is a passive upgrade to it.