This is an addon for Scrabx3's Alternate Perspective OR Arthmoor's Alternate Start - Live Another Life via patch.
Select the "I'm interred in a crypt" option to begin.

I Used to Be a Dungeon Boss like You
I Used to Be a Dungeon Boss like You puts you in the cold boots of a dungeon boss in a crypt on... wait, are none of the mountain ranges named? A mountain south of Winterhold city, only a short jog away from the Shrine of Azura or Mount Anthor. You're given a mostly complete set of ancient nord armor, an ancient nord waraxe of the cold, and access to the frostbite spell and set loose on the world.

Why? Perhaps you were put into a magical slumber for some long-forgotten crime. Perhaps you were dead, but resurrected by some mechanism of the crypt. Perhaps you were a powerful lich, *start option does not confer lichdom, or maybe Alduin flew by and awoke your immortal dragon-soul. The scenario imagines that you have no memory of being entombed, so the reasons for your being are up to you.
Your first challenge will be slaying the looters in your crypt, from there you are free to explore Skyrim to your leisure.
As with Alternate Perspective's normal scenarios, you can start the main quest.

If you choose not to use the start option, the crypt will be a low-level dungeon instead. No player characters will ambush you, probably.
The dungeon is fully navmeshed and the mod is cleaned in xEdit.

Requirements
Technically, thanks to the magic of PapyrusUtils and UI Extensions, neither Alternate Perspective nor Alternate Start: Live Another Life are required for the main file to work, but without one you'll just have a fairly short amateur dungeon in the mountains. In order to actually use this mod as intended, you will need one. The Alternate Start patch requires Alternate Start.
Alternate Perspective itself requires PapyrusUtils and UI Extensions.

Installation

• Download and install Scrabx3's Alternate Perspective or Arthmoor's Alternate Start - Live Another Life.
• Download IUtBaDBlY, and the Live Another Life addon if you are using that mod.
• Extract zip to data folder or install with mod manager. Live Another Life patch should overwrite/merge with the base mod.
  

Speculative FAQ

• Why is the dungeon built with Soul Cairn architecture? Isn't that *gasp* unimmersive?
  Soul Cairn architecture was just what I felt most motivated to use, I didn't think much about lore when using it. It was very easy for me to make a cave or nordic dungeon too big, and I've always liked the look of Soul Cairn architecture. Perhaps the dungeon and its occupant have some relation to the Ideal Masters of the Soul Cairn. I don't know. None of the architecture from Dawnguard is consistent with the rest of the game.
• Will you be adding more crypts to start in?
  I might do more in the future and I'm certainly interested in doing more Alternate Perspective addons, but I am not sure it'll be as an update to this mod. I might have done some things differently if I was always developing with the intention of expanding this mod, and I might not provide an ASLAL patch for them since I won't be using it myself going forward.
• Help, the adventurers keep killing me!
  Well, now you know how it feels. There's some useful potions in the cramped hallway before the second adventurer, to your right in a vase. You'll still have to kill the first adventurer, I'm afraid.
• Can I just live in the crypt?
  After completing the quest, the crypt will function as a home, and shouldn't respawn (if I did this right). It wasn't a priority for this mod, though, it's not fleshed out and I wouldn't recommend it.
• Was that a pun about skeletons and their lack of flesh?
  Yes.

Credits
I'd like to thank Arthmoor for Alternate Start: Live Another Life, which this mod began life as an addon for. Arthmoor's guide and example for creating an addon to that mod was my introduction to Papyrus scripting.

I'd also like to thank Scrabx3 for Alternate Perspective, which was less frustrating to script for because it didn't need an ARTH_LAL_StartQuestproperty which causes the Creation Kit SE to freak out despite being compilable Papyrus (I ended up casting it), and thanks to the implementation using UI Extensions it didn't even need a TIF_ script, which are much more annoying to make than QF_ scripts because Creation Kit.