Interesting. Basically have a mech that motivates you to not gain XP, beyond a minimum you need to kill your target. That's very AIW.
If the math worked I'd say something like "All enemies start with -90% damage, but each level you gain gives all enemies +20% damage" or something like that.
But damage numbers are very coarse so it doesn't seem like that would work.
Something like "Enemy spawn rate -90%, but each level you gain increases enemy spawn rate by +20%" would be even more appropriate, but I don't think SR's room designs work with the idea of increasing or decreasing enemy spawns on that basis.
Something like "All enemies and enemy shots slowed by 90%, but each level you gain increases speed of enemies and enemy shots by 20%" would work mechanically and probably work balance-wise, but it doesn't make a lot of thematic sense and kind of horns in on the Redshift's deal.
Something like "You start with +100 health, but each level you gain decreases your health by 20" would also work mechanically and maybe balance-wise, and would kind of accomplish the same idea as the -90%-enemy-damage rule, but it doesn't make sense thematically.
Taking a step back, how about something like this:
- Every level you gain increases enemy spawn rate by 20%.
+ All shop items (including sac items?) are free.
So you can gain a lot of power by reaching the shops (like you can in AIW from Advanced Research Stations, Advanced Factories, Design Backups, Turret Controllers, etc) but reaching them involves clearing rooms, which involves killing enemies, which involves gaining XP.
The spawn rate increase would just mean randomly picking X% of the spawn points and having them spawn a second/third/whatever monster. I think that mechanic already exists. But maybe it's just too much of a pain?
If so, the spawn rate could be replaced with an enemy speedup.