his village is one of magical adepts, each specializing in some sort of element, and those elements are used in day-to-day life as well as combat. Finnian's a Fire mage in training, his fire occasionally backfiring and leaving him a soot-covered mess. possibly bereft of a sleeve or worse.
his tail was possessed by a spirit, which caused him to become the tailmouth he is, and simultaneously get him banished from the village...despite the spirit not being malicious, but rather the sort to bother shut-ins and get them outside. it tried to fully possess him, but couldn't get much farther than the tail, and found itself stuck there. the spirit can use his magic, but it effectively needs permission from Finnian to use it. otherwise, it's totally autonomous.