Man, Scarlet Rot can do some work.
CARLET ROT EFFECTS
Targets afflicted with Scarlet Rot lose
HP and take damage.
MORGOTT, THE OMEN KING COMBAT INFORMATION
That's ~47 damage per second over 90 seconds, i.e. ~4250 in total. I fought this guy in the most pussy way possible, I opened up with the Decay and just ran around him, poking him with Bloody Slash only when he would do his jump attack that's extremely easy to evade. The fight lasted well over 90 seconds because of it. One successful proc melted away 40% of his health and I didn't have to use a single Flask during the entire fight because of how safe I played it.
I kind of regret killing him this way, he didn't seem too tough, I believe I could've taken him out in a more non-pussy way after a couple of attempts, but he was a good trial run. Now I know there's a safe way to kill even the toughest bosses, should I ever get stuck on one, as long as they're not completely immune to the Rot.