The text on Path to the Grave says you can mark another creature’s life for termination. But it also says as an action to choose “one creature you can see”.

Can I self-select as a PttG target? If so, can I use Life Transference to 2x the dmg I take (and thus 2x the heals)? You can curse yourself with Path to the Grave, but it only gives vulnerability to the next attack from you or an ally that hits the cursed target. Life transference isn't an attack.

— Dan Dillon 👥 (@Dan_Dillon_1) January 26, 2020

Ooo I thought I was real clever there I like where your head was at. 🙂

— Dan Dillon 👥 (@Dan_Dillon_1) January 26, 2020