(from a comment on G+ that got too long)
+James Brigham asked on G+: Our wizard casts Charm Person at +6. It regularly occurs that she casts so high that only a natural 20 can save – and the check is repeated only in weeks or months. I know the game is not about balancing, but this seems wacky. Or maybe I got it wrong? (correction, James says it was originally Oliver Korpilla’s question and he was just sharing it)
A couple things to think about before you decide it’s OP:
1) the wording of the spell is that the target “falls under the caster’s complete control, as if it were his friend.” As Judge, I would emphasize the friend, not the control; there are strong limits on what people will do even for trusted friends, and the more evil the character the more likely they will be willing to betray or even murder a friend under the right circumstances. Rather than altering the mechanics of the spell, work through the role-playing aspects of it.
2) The spell grants no extra ability to communicate with the target. Maybe you’ve charmed that Reptile-man, but have fun pantomiming what you want him to do. (No, really, have fun with it: make them act it out.)
3) There are penalties for trying to apply it to anything except standard mundane humanoids, and it’s entirely up to the Judge what counts as mundane. Depending on your campaign by the time characters are at levels where >20 DCs on the checks are routine, a 0 or 1st level mundane humanoid doesn’t pose much of a combat threat anyway. If they could kill someone easily, then it’s not particularly worrisome they can befriend it instead as long as you don’t let them turn their friends into complete puppets. If the target is high enough level that’s not true, it’s high enough level that it may have some magical protection against spells like that or boosts to its Will save beyond Per Bonus + Class Bonus. Or be able to cast that spell against the players. Which leads to
4) it’s a core principle of DCC that NPCs and monsters aren’t limited to following the same rules as PCs. If you’re really having a problem with the players blowing through things that you thought would be fun and challenging by befriending everything in sight, consider what kind of situations you could put them in where that wouldn’t help. It could be as simple as if they can neutralize/ally with 2d6 humanoids per round it’s time to up the stakes to adventures where there are potentially hundreds of humanoid enemies if they play recklessly. Or perhaps the next enemy employs automata that are immune to charm. The point isn’t to thwart them so much as to only play out the stuff that’s interesting because it’s hard for them. Treat the encounters they can just charm their way through as routine.
5) Try to work out the logical consequences of things and if they seem to be a problem consider how the world would react. If you look at a spell like Charm Person and ask given that, why are there any kings as all that aren’t under the thrall of some 3rd level Wizard? it’s up to you as Judge to make that work for you. Maybe you only get to be (or stay) king if you have some kind of magical protection against that sort of thing; maybe the very fact you’re king grants you a blessing from the gods of the kingdom that protects you; maybe successful kings are paranoid and don’t let strangers within casting distance of them; maybe some are in thrall to their court wizard and anybody attempting to charm the king has to deal with that wizard, etc.