"The flaming hound"
Describe the myth surrounding a creature in your world It is a well known fact that wizards create all kinds of abominations. Some are cute and harmles, others are quite a threat to humanity. One of the most well known creations of wizards of yore is the owlbear- a massive owl and bear hybrid. A dangerous creature, yet a timid one. However then a different old mage went too far. It is said that the wizard took an owlbear, sent it to the nine hells for a few days and called it back. This happened multiple times. Eventually the mutated owlbear was a shambling mess on all fours, burning all over, looking more like a hound than a bear. The tortured giant hound went around in beastly panic, burning everything in it's wake- villages, forests and shrines. At a certain point, after the flaming hound calmed down a bit, it looked at the destruction it sowed- and smiled. The destruction made it feel just a little better. After running around Soderhalm, burning everything it could see and even mating with multiple owlbears, the hound was captured by the ancient warrior wizard Lysithea of line Goetia. As punishment, the locals decided to burn the wizard that created the flaming hound with it's flames, before putting the hound out of it's misery.
While the wizards name (Anatoli) was lost to time, it is rather accurate to he original story.
Variations & Mutation
Many claim that the basis for the slaghound, a creature that exists today and is thought to be the flaming hound, cannot be an owlbear. Some say it was a manticore or perhaps a dire wolf, others claim it is a plain old hellhound with some extra steps.
Many books for children include the slaghound- usually as a monster for the hero to defeat. It is usually picked for it's vile nature and lack of redeeming qualities.