My campaign is set on a low-magic setting, meaning magic is not common. Magic users are generally welcome, although at some places they hate magic users.
Most (80%) of my players start off as a magic user, sorcerer, warlock, wizard, ranger, bard, arcane trickster, eldritch knight, etc. despite this premise. I allowed (so many of) them, but reminded them there might (or will) be consequence later for magic users.
Now I’m at the point of revealing that magic taints the world, and thus must be very carefully used, unless they want to permanently worsen the corruption. Because of this, I expect the players to opt not using magic at all, including magic items. The party is at level 4 now, and I expect them to reach 5-6 when this happens.
How to balance combat encounters to be level appropriate, if, in worst case, they won’t/can’t use magic at all?
The party relied on two warlocks to deal AoE damage on previous encounters. If I’m to use several lower CR (CR 1 or 1/2) monsters, I’m worried that they might be overrun by the monsters. On the other hand, if I use one or two monster with more CR appropriate, I fear they are too powerful because of their abilities. I can tone down the HP or attack/damage/abilities, but I’m trying to preserve their original statblock as much as possible, even including resistance/immunity to non-magical piercing/bludgeoning/slashing damage.
I’m expecting 5-6 people per session from a pool of 10. Only two of them goes pure non-magical path.
Although the question is how to balance combat encounters, I’m also open to solution that does not directly modify how encounter works, such as suggesting to multiclass ahead of time (I’m currently planning this as a last resort, though).
Note: Corruption is a term I use to explain mutation of nature. When first understood, it is framed as a bad thing. It does not, however, kill the land, but it alters nature to something “unworldly”. The simple thing is appearance of giant spider and worm is a mutation from the normal spider and worm.