Something that has always bugged me is the enormous power jump most creatures get when they become undead. Sure, some of it makes sense, with new abilities and sinister powers. But what has never made sense is the immunity to all mind-affecting effects.
Tweak: Mindless undead with no Intelligence score are immune to mind-affecting abilities as normal. Intelligent undead lose this immunity.
While it makes sense that you’d be unable to use Charm Monster on a zombie, why is a vampire treated the same way? And before you start thinking “well, undead just aren’t controllable,” don’t forget about clerics and Rebuke. There’s also a spell called “Control Undead,” which is, of course, not mind-affecting.
While this tweak is a very significant power loss for many undead, I don’t believe it is a bad one, because it simply opens up options for the players. Undead still have Will saves. This just allows Enchanters and bards to do their thing in more situations.
Another option would be to do away with the concept of immunity entirely, as a gradient of strengths and weaknesses are always far more interesting for gameplay.
Enjoy slaughtering the already dead!
-Max Porter Zasada