Sangrazul
Sangrazuls are an anthropomorphic race which have the ability to find mana lines better than even planeswalkers.[1] As such, they serve them often. Currently there is only one known Sangrazul - Malvos, who served the planeswalker Tempé.
Sangrazuls have great longevity. They do, however, need to "eat" mana from time to time to survive. Death by starvation, though, is a long process. After at least five hundred years, starving Sangrazul start dying. It's very painful, and months of conscious horror can pass until the immovable, drying body releases its tormented soul. The craving for mana can be held off in the short term by the consuming of sweets, centuries of this behavior leading to morbid obesity.