[3.5] When does the [Mind-Affecting] tag REALLY become a problem?

[Zaq]

So, it's generally agreed upon that a spell that has the [Mind-Affecting] tag is generally weaker than one that doesn't, because immunity to mind-affecting things comes up so frequently at higher levels. (This is one of several reasons why so many people suggest that specialized wizards should ban Enchantment right after banning Evocation.) However, at lower levels, the immunity isn't quite as common. Certainly, there are some low-level monsters that have immunity (undead leap to mind, and it's not at all uncommon to see some skellies running around at 1st or 2nd level), but at what ECL does relying on mind-affecting abilities really turn into a major liability? At the highest levels, naturally, the existence of Mind Blank means that no one with spells or a friendly caster should be worried about these things (not to mention the natural immunities of a lot of creatures), but at the lower end of the spectrum, it's mostly just undead and vermin who can't be hit with it. When would you say that it becomes a real problem to have mind-affecting abilities be your main (not to say only) shtick? Why?

[Burley]

Well, I play a beguiler now. I'm ECL9, but I nerfed myself with two levels of Master of Masks. (I didn't want to step on the party's actual wizard's robe.)

I haven't had a LOT of trouble with it, but in the most recent session, some sort of snow swarm or snow ooze or something came at us. I was useless. Granted, I was short a few spell levels. Anyways, if it weren't for an Item I had which gave me access to a couple buffing spells, I might have just walked away and let the cleric handle it. Probably should have, just to speed things along...

[Saph]

In my experience immunity through creature type is a much bigger problem for an Enchanter than Mind Blank.

About 1/4 to 1/3 of the creatures you'll face in a typical campaign have the undead, construct, plant, vermin, or ooze type. This means about 30% of the time, Enchantment spells are useless. However, the remaining 70% of the time, Enchantment spells are freaking lethal. They all target Will, which is frequently the weakest save on monsters, and a failed save is usually enough to eliminate a monster entirely. A spell like Confusion can win an entire battle with just a few lucky rolls.

Now, once Mind Blank enters the picture, casters can pick up that immunity too. However, three points:

• Mind Blank doesn't become available until level 15-16 minimum. The vast majority of campaigns end before then.
• The only ones who can cast Mind Blank are level 15+ sorcs, wizzies, beguilers, and other casters who all have high Will saves, meaning they're already a poor target for save-or-lose Enchantment spells. So the only big difference it makes is stopping stuff like Irresistable Dance.
• Mind Blank can be dispelled, and dispelling tends to be a standard opening move against enemy casters.

In my experience, the reason more and more creatures have immunity to mind-affecting at higher levels isn't because of Mind Blank. It's because higher-level Enchantment spells are so insanely powerful that any BBEG who doesn't take precautions against Enchantment effects is likely to end up with his entire minion force mindslaved.