I'm running a campaign with a constant group of players and have been for a couple of years now, in which they are playing several generations of PCs, each consecutive generation being more powerful than the last so to experiment with how cool and flashy things can become.
The issue is that we're coming up to the absolute limit of what is allowed by the standard rules. The obvious solution here is to just "bring everyone back down to base and start over", but the reason that everyone seems to enjoy it so much is because everyone has such overpowered bullshit that it ends up balanced precisely because everyone has overpowered bullshit, so if I nerf them when we hit the ceiling I can see everyone inevitably becoming so disappointed that they lose interest.
The best solution I have come up with involves a kind of magic named Sions, which are kind of like spells, save for that a character can only have one and they are disgustingly open-ended because they function on a conceptual level (e.g. having a body in "another world", being able to "freeze" things, making anything "rotate") as opposed to a physical one.
But because they affect concepts, which can't be quantified, I have absolutely no idea how to implement it into this system. Have I dug myself too deep a hole or is there actually a way to handle this?
The system itself is homebrew and percentile, based almost entirely around magic. The spells themselves are created by the players using the five traditional elements (which they may know how to use any combination of; for instance, fire and earth is used to make magma and air and water is used to make ice) and this is balanced by the cost being directly proportional to the power, effectiveness, accuracy, difficulty, and additional effects of the spell in question. Ideally, I'd like Sions to be dynamic for versatility, as opposed to the video game-like "specific action" that spells are, and I definitely don't want to weigh them down by categorising them into elements.
The stats the system uses are Potency (magical output that functions like strength), Dexterity (accuracy and flexibility), Agility (speed, ability to dodge), Endurance (HP and defence), Creativity (spell creation, MP regeneration), Intelligence (spell creation, deduction), and Awareness (basically what it says on the tin). The cap for base stats is 100, but due to the fact that stats can be raised as high as 170 if you munchkin hard enough, there's a lot of division and multiplication involved as opposed to addition and subtraction, with the only exception being hit chance, which is the Volatility (reverse accuracy) subtracted from double a character's DEX.
Mostly, I'd like to know if this has been done, or at least attempted, in any kind of dice-based system and how effective it was. What I don't want to do is tie it into the rules that were designed for spells, because that would both result in Sions becoming exactly the same as spells and opening a ton of holes that I won't see. A couple of ideas I've come up with myself is to give the Sions some stats of their own, like PTC, to determine what they can and cannot do with their absurd versatility; simply sitting down with each player to work out the rules separately with each; or giving Sions spells of their own that just take priority over other spells, albeit the latter seems a bit dull. If any of these work, which would work best, and should I allow players to affect things on a conceptual level with them (e.g. freezing a person's HP to make them immune to damage or rotating their alignment)?