This fella is a re-design of one of my demon concepts from earlier in the year.
Concept is that he would be summoned into an enemy village and if not dealt with and disposed of quickly he would spread in-reversable infection among the villagers.
Big/Slow. Not physically hostile. The Plague Beast simply needs to walk into the target area and reside there for long enough for his noxious fumes to do the their deadly work.