Spike Rot Frost Jaw is the type of splendid undead skeleton boss monster for which you have been looking. He was likely in your dreams - you just didn’t realize it. Likely, you mistook it for an evil snowman.
He comes with a very multipurpose background / lore that can be used as clues to the Player Party in discovering his whereabouts. Every DM can use a readily available random monster already created for use in a pinch to spice up a session if PCs are getting restless. Some may love you and some may hate you afterwards. Todd may finally stop talking about how his half-orc barbarian is a descendant of some great orc warlord and can kill anything. His orc may not like the cold, after meeting good ol’ Frost Jaw.
Creaky and frosty. Brutal and quick. This skeleton’s gone berserk. The now undead and once honored war hero from another time - it’s Spike Rot Frost Jaw!
- from the publisher's blurb