The Soul Sand Valley Shambler

The shambler inhabits the soul sand valley, and could be a replacement for normal skeletons (which I don't think fit very well, since they can be set on fire). Shamblers resemble large conglomerates of bone that are held together by a soul-fire core.

The shambler shoots more slowly than skeleton archers and moves more slowly as well, as it has to pull its weighted body along the sand. 

Shamblers shoot soul-fire shards from their mouths which will light the player on fire when hit. The shambler indicates when it's about to fire by opening its mouth. The closer to firing the arrow, the brighter-blue its mouth gets. Blocks hit by the shambler's soul-fire shards will be set on fire, even after being deflected by a shield. 

Shamblers can be set on fire, but will take no damage and will burn with soul fire instead. If the player gets too close while the shambler is on fire, they too will be set on fire. The shambler will also spread fire to nearby blocks when low health. When the shambler dies all the fires it set will disappear.

Shamblers would drop bones and more experience than skeletons.