What exactly is that Sirus "death storm" damage type?

if its a physical dot you should see clips of things like RF juggs with RF turned off just afk in it, i've been trying to work this out and settled at a damage split for now.

Poe database has almost all his attacks listed as physical damage, with like 20% converted to fire, lightning, cold, and chaos. So 20% of everything, I guess.

Whether that is also true for the storms I'm not sure.

First few times I fought him I had -40% chaos resist. Third time I fought him (and beat him) I changed some things so had +2% chaos resist, then did shakiri and arakaali pantheon, and had a flask to increase chaos resist. The lower amount of damage I took from everything was noticeable.