Really? What's this "decent wizard" that you're talking about? And which 4th and 5th level spells give him a viable chance of taking out the devil?
The "one spell, one creature" spells I can think of at those levels are: Charm Monster, Dominate Person (won't work), Dismissal, Hold Monster (nerfed to save every round now), and Phantasmal Killer.
So, let's take a "decent" 9th level wizard. Int 16+2 (stat increases)+4 (item); Spell Focus and Greater Spell Focus, Spell Penetration and Greater Spell Penetration (and we're assuming they weren't nerfed to +1 clvl for consistency's sake--IME they were more popular among generalist wizards and sorcerors than the focus feats).
To effect the Ossyluth, the wizard needs to roll an 8. So that's a 65% chance of success with any given spell.
To then effect the Ossyluth, with the spell, the wizard has a:
Charm Monster DC 22 vs +15 (including the +4 for an obviously hostile target)=20% chance of making the Ossyluth ignore the wizard or attack him for subdual. (Come on, he's Baatezu; just because he thinks the wizard is his friend doesn't mean he likes the wizard's companions).
Dominate Person: won't work on an outsider
Dismissal: DC 22 vs +12 (accounting for the HD difference between the Ossyluth and the wizard)=29% chance of banishing the Ossyluth
Hold Monster: DC 22 vs +11=33% chance of paralyzing him for one round (not that this does nothing to prevent the use of the Ossyluth's spell like abilities)
Phantasmal Killer: DC 22 vs +11 and +12=33% chance of dealing damage to the Ossyluth and a 14.6% chance of killing it outright.
If you go to wizards focussed on dealing damage rather than save or effect spells, most of them will have to deal with the Ossyluth's numerous elemental immunities and resistances as well.
So, the wizard can easily spend a lot of spells without effecting the Ossyluth. In fact, the best case scenario (an abjurer with 3 dismissals prepared, greater spell focus abjuration, and greater spell penetration (looking suspiciously like an optimized wizard for a highly unusual encounter rather than a "decent wizard")) has about a 69% chance of getting rid of the Ossyluth in three rounds if he casts all three of his 5th level spells. And I wouldn't call that a reasonable chance, considering that both the character and the spell in question are optimized and useful only in exactly this situation.
It's not quite "go home, you're useless" but another fighter or a barbarian would be far far more useful.
mmu1 said:
Oh, BS... (Or a complete exaggeration, anyway) In that particular example brought up above, a decent wizard would have something like a 25% chance of taking out the demon with a 5th level spell (with 3.5E Spell Focus), and demons have pretty much the best saves and SRs in the game. That means with a 4th level spell, which he has several of, he'd still have a viable chance...
Then there are the spells that don't give a save, do partial damage, affect mobility... And since when is it beneath a wizard to contribute to an encounter by using protective spells? What, that's good enough for a cleric, but a wizard has to be able to blast anything and everything with a damage or save-or-die spell?