Potion Effect (Or anything in general) that affects attributes or can detect damage taken and dealt?

Basically, I want to make a Potion Effect that doubles the damage you deal and take (Calling it Berserk), which would be made with a drop from a boss mob I have in my mod. Problem is I have no idea how to go about this since you can't use source entity stuff with Potion effects, and I don't want a Potion that just gives other existing Potion Effects (Not that taking double damage is an existing one anyway). Any ideas how I would go about this? At the very least, I need to know how to make the effected entity take double damage since that doesn't already exist as an effect, and I'll just have it apply two other effects if I absolutely need it to (Not ideal, but whatever).

(2021.1)