Jack Frost is a boss in Slender Fortress.
During the Twisted Christmas update, it is suppose to be a re-skinned Husk so it will look like a snowman. This skin depicts a stereotypical snowman, albeit slightly melted, complete with stick arms and legs. Its mouth seems to glow slightly, and its right arm seems to be a stick that can throw flaming "snowballs".
In Slender Fortress Edit
Jack Frost is a ranged chaser in boss pack 1 he instead of shooting icicles or frosted things he shoots fireballs for some reason he is similar to Archvile and Huskotron in that he also has a melee attack as well he is stunnable and it's a 2 second stun so you can rely on that to save you if he becomes a problem.