Guild Wars 2

Anyone know how Life Siphon works? Like what stat determines the amount you get healed? Is it based on the amount of damage you do or is it based on healing power?

It’s never based on the amount of damage. It’s basically always depends on what level you are + some minor things that get count.
GW2wiki:
-Life Siphon heals for 202 per tick at Lvl 80, and increases by 1 per 25 Healing Power (approx.)
-Siphon Health from Vampiric is capped at 25 base, it gets to 38 with Bloodthirst. It doesn’t scale with power or healing power.
-Siphon Health from Vampiric Precision heals for 31 (without Healing power)

Even geared for heal power +regen 100% uptime with siphoning well pulses the siphon build doesn’t, to me, feel up to par. Lack of ally healing through siphoning, other boons (primarily vigor, imagine what that could do for necs) and the list could go on. But I’d be happy to have ANet take a look at some scaling of heal power in regards to blood magic trait line.