Thanks for all the answers
I've noticed the effect of negative damage before, but always figured that if you outdamaged the regen it would counter the negative damage. What I mean is that now the negative damage seems to stack, but the postivie damage seems to be constant. Instead of both of them being constant or stacking, which to me would be logical.
So the way I understood it works now is:
Creature starts with a hp of 2000. This is the amount you can deal positive damage to it and no more (or maybe the highest hp amount the creature can have?). Even if you actually deal a lot more due to the regeneration.
On the other hand the negative damage stacks, so if the enemys creature managed to heal 10000 damage before dying, you'd end up with -5000 damage?
Because if the positive damage stacked like the negative does, I would always end up with positive damage that would match the creatures starting HP. If the creatures lose 100% of their HP that is.
Anyway that's the way I understood it from the battle I posted above.
But it's good to know that it's at least frowned upon Puts my mind at ease a bit.