Something I am curious about: Are there any mods (for either game) that replace the leveling system with something bizarre?

Here is what I *don't* want:
* I don't want something similar to the default leveling system.
* I don't want one where you gain stats depending on the skills you use.
* I don't want one that replaces the leveling system with an XP system.

Rather, I am looking for more unusual mods. Like, maybe having which stats increase be totally random, or have stats grow with completed quests or treasure obtained, or get stats based off which items and spells you have equipped, or gain stats based off the enemies you kill, or something more bizarre.

Any mods like this out there?

(Joke mods are OK if they are labeled as such and primarily affect the game's leveling system.)

I don't remember any mods of this kind myself, but perhaps this link contains some information:
https://www.reddit.com/r/oblivion/comments/kj97b/best_leveling_mod_for_oblivion/

Oblivion has a dreadful level up system where you need avoid levelling up some major skills while you grind on others in order to get your +5 in certain traits (strength, intelligence, willpower, etc) at level up. This is really distracting and annoying. I used the mod "All+5AttributesModifiers" by Falconhurst worked really well and I recommend it. Also try Soul Gem Magic.by The NiceOne. This allows you to completely fill a soul gem that has a small soul in it. Eg: If you have a Grand soul gem with a petty soul in it, if you capture a, say, common soul, it will go into the grand soul gem next to the petty soul. It takes 5 greater souls to fill a Grand soul gem. Not sure how many mud crabs you'd need for that! lol

Nothing like that exists... there is one thats a super cheat of sorts where you pick your level at creation and are frozen in time

But if you truly want the best leveling mod to get rid of the craziness thats is Oblivion then Oblivion XP Update is it... nothing better, and as you requested this mod adds a few features you might like ^_^

That mod does seem like an interesting idea. The idea of using potions to level up stats actually reminds me of SaGa 1 and 3 (specifically, human leveling in SaGa 1 and robot leveling in original SaGa 3); just lower the cost of stat up potions and have it be the primary method of stat growth.

It might be interesting to have a mod that does that, but keeps skill leveling the way it is.

Weird thought: Could a mod be made that gave the player an ability to copy an NPC's stat and skill list, and make it the *only* method of getting stronger (and perhaps weaker)? Bonus points if this copy also gives any special abilities the target might possess. That would be accurate, except for the fact that my pronouns are she/her (see my forum title).

I just remembered an interesting Oblivion mod which doesn't change the levelling system, but the monsters and their levels. More precisely: It randomizes them. Especially when your character is low or medium level, this mod guarantees some creepy moments, and you'll be running away a lot (or reloading :-)). Not exactly what you are looking for, but bizarre enough, I guess. I like it because it does away with the sudden change of monsters every 5 levels, and because I find monsters which adapt to the player's level automatically boring.
It's called "Random Oblivion" and was created by Talonhoff - and it's hard to find nowadays. The most recent version I have is 2.1, but all I could find today was 1.1 - shouldn't make a big difference, though.
Here is a link (which I myself haven't tried): https://www.gamewatcher.com/mods/the-elder-scrolls-iv-oblivion-mod/random-oblivion-1-1-mod

And here are a few sentences from the mod description:
"Welcome to reality, fear, and excitement. This mod completely changes the world of Cyrodiil. Now almost all creatures are random levels and have random loot. And now most treasure is random, too. What this means is that when you start a new game, you must be very, very careful when adventuring. You could encounter any very low to very high level creatures when you character is at ANY level. But, the rewards are much greater now. You can get very high level items early in the game if you are lucky. You will need these higher level items just to survive the game. It is advised that lower level characters stay out of dungeons and other dangerous areas until leveling up a little bit. Pearl diving is a safe and profitable alternative in the beginning. You may now buy any level weapon or item from any vendor regardless of your level.
The reason why I did this mod is to help create a world of adventure, realism, suspense, and danger. The original Oblivion world adjusts to your character's level. But that's not like the real world, is it? It's always fun to go adventuring, and not knowing what may be lurking around the next corner. The thrill of being chased by several high level creatures that can snap your neck in two hits is quite exciting. A good (and safer) way to make money early in the game is to steal from people in the towns and sell the stuff for a profit."

though scripts you could query an object for skill level and known spells. then run the numbers though a simple formula and add them to yourself with a chance modifier... i have no idea how to do this but it can be done...

that said, i did make a spell that made everyone in the current cell naked and 100% aggressive to each other and called it "Party Hard" it was my greatest achievement ever... i also have a version that changes the sky to oblivion and plays dubstep music.

My apologies; I normally use "they" to avoid just this problem.