SL1 hyper mode, bby.

+20% damage with HP loss (Power Within)
+20% damage at 20% HP or below (RTSR)
+20% damage at 20% HP or below (Morion Blade (assumption based on RTSR's bonus))
+10% damage (Dragon Head roar)
+10% damage (Flynn's Ring bonus when naked)

1.2 x 1.2 x 1.2 x 1.1 x 1.1 = 2,09 = a 109% damage increase at 20% HP.
If I decide against using Power Within (since that's a very small bonus for the HP loss), it's still:
1.2 x 1.2 x 1.1 x 1.1 = 1,74 = a 74% damage increase at 20% HP.

Couple this with this game's Raw infusion being really good. We're talking like 40% extra base damage than a normal upgrade path, with no scaling, so it's perfect for SL1 runs.

If I really wanna go overboard, I could even add Resins into the mix for even more damage (since Raw is a buffable path), but since we don't have exact damage bonuses for these yet, I left them out of the equation for now.

Tl;dr

SL1 hyper mode is gonna be fun.