What about:
* All stats (including things like HP) come from equipment, and you don't have body slot limitations (so you can wear 2 suits of armor at the same time)?
* You kill an enemy and get a small portion of their stats? Possibly even learn an ability that way?
* You have some special abilities that, if used to inflict the killing blow, will give you a stat boost and an ability? (Catch: You can only have one enemy absorbed per abilitiy, and using the same ability to absorb another enemy will replace it.)
* After each battle, you have a chance of a random stat increasing my a random amount?
* You start out powerful, but as you use your abilities, they become weaker?


See the post I just made in this topic.
You can have classes without levels.

Also, the term "class" has a name collision in some programming languages; in many languages, like C++ and Java, you can't name a variable "class" because "class" is a reserved word.

I don't like classes. They're confining, and prevent you from being able to do and mastering more things, and even experiencing all the game in one playthrough at times. So classes may work in party-based games, more so with larger parties, 6+. But with single character games? Nope, give me full freedom and no limits, either train through use or by spending exp and have places where I can grind for exp (but not infinite respawns everywhere, that just makes it feel pointless to clear any area, just have some specific areas with infinite respawns).
Ew, no way. Why call it an RPG if there's no actual character development? And no limitations on gear slots is way too weird. Draining stats or abilities from enemies is a rotten mechanic, reminds me of FF8 in that way. I won't even begin to say the sort of bad feeling that idea of special abilities that can generate others if used in certain circumstances triggers in me. And no randomness, definitely not in that sense. Ffs, I'd save scum and reload after each fight until I get just what I want then, never get past the starting area probably. The last thing sounds like To Ash. Grabbed that when it was free, but rather dread to play it...

What about a Final Fantasy 5 style job system? Or even a Final Fantasy 3 one?

* In FF3, jobs are like classes except that you can change at any time outside of battle (unless you're low on CP, which is rare and only happens in the famicom version), but you only have the abilities of your current job.
* In FF5, it's the same (minus the CP), but now you can learn abilities by gaining AP while in that job, then use one of the abilities you learned in a different job.

Nope. Still limiting for one, for each moment if not in general, and I'd keep wanting just the perfect choice each moment then. Well, either that or try to find one that's best overall and stick just to it if possible. Either way not use it as intended, definitely no way.

Or, something like the Hatchet Man ability of later Dragon Quest games (6 and onward), which will either score a critical hit (very useful against Metal Slime type enemies, because you'd do 1 damage half the time otherwise), or fail to do damage entirely, perhaps?

(Note that Metal Slimes really are a special case, as they have an unusual combination of characteristics:
* Low HP, like 3-4 for basic ones, and even the strongest one has only 7 in its earliest appearance, only getting more with the appearance of Hatchet Man.
* High defense. High enough so that your attacks will only do damage half the time, and even then it will only be 1 damage. (Exception: A special weapon or skill might be able to consistently deal 2 damage.)
* Are outright immune to magic. (Occasionally there will be exceptions, but generally those exceptions are attacks that would remove the enemy without giving you XP, and you don't want to do that to a metal slime.)
* Like to run away. Note that these do not always let *you* run away; you could fail to run away, only to have the enemy run away (which always succeeds).
* Are not particularly dangerous (although DQ5 ones can cast Chance/Hocus Pocus, which has random effects, including one that paralyzes everyone (which is actually good if the wagon is with you)).
* If you manage to kill one before it runs away, you get tons of XP. Metal King Slimes can give you over 30k XP (per character) if you manage to kill one! That's far more than any other non-boss enemy; even entire groups of late-game enemies only give you a few thousand (assuming no (Liquid) Metal (King) Slimes are killed).
)

But all of what you just said just translates into RNG deciding everything. Need to get enough damage rolls to go your way before the slime has a roll that makes it flee. Crap design there.

If you're talking about my mention of Dragon Quest metal slimes, they're a very special case.

There's only 3 enemies in the entire game like this (fewer if we look at DQ1-3), and the only reason to fight them is for the extra experience. In particular, if you just want to beat the main game, you don't actually need to kill any of them (though you might want to kill one if it happens to appear). It's really only power levelers who need to hunt them down, and even then, it's not until DQ3 where I'd consider it to be a good strategy.

(By the way, endgame leveling in DQ2 is fun; you're facing really powerful normal enemies, some of which have multi-target instant death or other nasty things. You end up having to find a different strategy for each random encounter, as well as being able to react to the situation (like if the enemy gets a critical, and you don't know if your status spells are going to work, but sometimes they're the best option). You will die some of the time, but fortunately, you get revived at the nearby shrine minus half your gold, and unless you're playing the original Japanese release, the priest there will revive your entire party for free.)

Also, supposedly Yuji Horii was into gambling, which is why you see the Metal Slimes and their relatives in the games, and also why you see casinos that favor the player (which are nothing like real life casinos in that respect).

Edit: You probably should not have cut the entire post I made in your post, as it makes it hard to tell what you're referring to,