So, let's say we've got a character who can learn both Wizard's and Cleric's spells up to 9th spell level. The said character knows that he will face something that deals massive damage (and, by additional rules, it makes him roll Fortitude so he just does not die right away) and wants to find a way NOT to roll that Fort regardless of amounts of dices that will be thrown at him (so he, you know, dies if his HP are less than -10), and preferably at least for several minutes. What spells can he use to do that exactly?
The rules of massive damage are:
If you ever sustain a single attack deals 50 points of damage or more
and it doesn’t kill you outright, you must make a DC 15 Fortitude
save. If this saving throw fails, you die regardless of your current
hit points. If you take 50 points of damage or more from multiple
attacks, no one of which dealt 50 or more points of damage itself, the
massive damage rule does not apply.
The amount of HP cap steps by 10 for every size category different from Medium (not that it really matters in the question), and as far as I understand, if one wants to cancel the Fort roll, he has to be immune to crits at all (through, I may be mistaken about it).
This is not question about invulnerability/invincibility, so those won't do the trick. Damage Reduction won't do it as well. No magic items or even a slight failure chance
Best Answer
Acquiring Immunity to Death from Massive Damage Is Weirdly Difficult
Immunity to precision damage or critical hits doesn't make one immune to death from massive damage. Having the elemental, ooze, or plant type doesn't make one immune to death from massive damage. A creature under the effect of the spell gaseous form [trans] (PH 234) isn't immune to death from massive damage. Even becoming incorporeal doesn't render one immune to death from massive damage. Apparently, massive damage is supposed to kill living things, and the way to become immune to massive damage is not to live.
That means immunity to death from massive damage can be gained only from the 7th-level Sor/Wiz spell body of war [trans] (SpC 35), the 7th-level Sor/Wiz spell undead mask [necro] (SS 71), and the 8th-level Sor/Wiz spell veil of undeath [necro] (SpC 229).
The mask and veil leave the target's type unchanged but grant many undead features, including immunity to death from massive damage. The body grants the caster, by turning him into a warforged titan, the construct type, hence immunity to death from massive damage; the caster can't cast--even via magic items--while affected by the spell.
So, um, yeah. That's it. That's all of 'em.
You can go sideways. Use the spell magic jar [necro] (PH 250-1) to move your mind into a body that's immune to death from massive damage or the spell polymorph any object [trans] (PH 263) to change form into a creature (or sandwich) that's immune to death from massive damage, for instance, but of the thousands of Wizards of the Coast spells published for D&D 3.X no spell exists that simply says, "You're immune to death from massive damage."
What You Can Do