Vampirism - You don't need to eat, sleep, or breath, but you must drink blood. Allergic to sunlight. Powers and weaknesses develop as you drink more people.
A character of mine in a Finders Keepers game currently has this trait. The question remains, what kind of powers and weaknesses will a vampire develop? You can use the generator below - once you drink enough blood, press the button and you will gain one random power and one random weakness.
While the powers and weaknesses were created with Finders Keepers* in mind, they can easily be used for vampiric characters in any Into the Odd-style game. To make it work as a GLOG class, you could grant Vampirism and one roll on the generator at template A, then one extra roll each level. Or just use it to inspire powers for your NPC vampires.
Dead blood is any blood removed from a living body for over an hour, or taken from a dead body that already started to grow cold.
To feed someone your blood, take d4 damage unless otherwise specified.
*) Some of the abilities are frankly stolen from there.