WHAT'S GOING ON?
One of the design challenges of Demon is figuring out ways to challenge the player that don't subvert the basic premise and don't lead to an arms race I'm destined to lose.
The basic premise of the game is, of course, "you can recruit your enemies and learn their abilities!" It's pretty fun, I think. It'd be good to not subvert this!
On the other hand... since you CAN recruit your enemies and CAN learn their abilities... this means anything I throw at you, in theory, you will shortly have to pick up and throw right back at the game. So that leaves out the usual options roguelikes utilize like, for example, throwing 'out of depth' monsters at you, if I throw you such a monster, you immediately have it to use: in effect you kind of become out-of-depth yourself. A similar problem arises with scary abilities: If I add a demon with say, Petrification, I've just given it to any player who encounters one. Interesting problem is interesting.
I had thought that Demon's balance was such where I could throw a few of these around now and then and it would be no more disruptive than say, finding a good random artifact in most roguelikes. Sure, it makes you a little more powerful for awhile, but eventually you outgrow the demon and the advantage is lost.
But, I'm starting to see some problems:
1) My desire to throw higher-level demons around as a form of challenge has made them a fair bit more common than "good random artifacts" are in most roguelikes. Rather than being a rare and exciting occurance, it may be impacting the overall challenge level much more often than that.
2) Even the ones I do use, I can only make somewhat higher level, because even one demon that was WAY over level would be way too much.
3) There is a bit of a steamroll factor for sure. Since many capture mechanics are based on combat performance, getting a strong demon early will help you get more strong demons that you might have otherwise failed to capture.
So, let's get to the meat of it:
PROPOSED CHANGE
Restrict Summoning of non-unique demons to those which are your level or lower. You may still freely recruit, Copy Abilities from, Fuse, Consume, Recycle, Soul Armor, etc. any demon. The only restriction is literally on Summoning. This would also apply to enemy summoners of course. Finally, demons currently over your level would gain 0 XP until you caught up.
The hope is that this would still give some benefit to recruiting higher level demons (learning their abilities, fusion possibilities, etc. seem to still be pretty strong arguments for recruitment), while avoiding completely subverting the main premise of the game, and also keeping the acquisition of these powerhouses from becoming more steamrollery than people (including me) seem to prefer.