An intensified disintegrate with an impossible save would sure be scary, though. Typeless damage! 2d6/caster level!
I've been thinking over the
disintegrate profile from level 21-40, looking at builds for 1-round delivery - primarily as a gauge for scaling the SP of spells which use the
destroy seed. There are lots of combos. They all get pretty nasty.
e.g.
Assumes Maximize, Empower and Quicken are taken pre-epic. Average damage on failed saves at the end of each entry.
Int requirements are very modest in this build until Lvl 38.
Lvl 21: Int 30, Improved Spell Capacity (10th): 1 x Maximized + 1 x Quickened (380hp)
Lvl 23: Int 30, Multispell: 1 x Maximized + 2 x Quickened (520 hp)
Lvl 24: Int 30, Improved Spell Capacity (11th): 1 x Empowered Maximized, 2 x Quickened (590hp)
Lvl 26: Int 34, Improved Spell Capacity (12th): 1 x Empowered Maximized, 2 x Empowered Quickened (730hp)
Lvl 27: Int 34, Improved Metamagic (-1): 1 x Empowered Maximized, 2 x Quickened Maximized (790hp)
Lvl 29: Int 34, Intensify Spell: 1 x Intensified, 2 x Quickened Maximized (960hp)
Lvl 30: Int 34, Improved Metamagic (-2)
Lvl 32: Int 36, Improved Spell Capacity (13th): 1 x Intensified, 2 x Quickened Empowered Maximized (1100hp)
Lvl 33: Int 36, Improved Metamagic (-3).
Lvl 35: Int 38, Improved Spell Capacity (14th): 1 x Intensified, 2 x Quickened Intensified (1440hp)
Lvl 36: Int 38, Improved Metamagic (-4)
Lvl 38: Int 44, Multispell: 1 x Intensified, 3 x Quickened Intensified (1920hp) [Headband +12, +9 Level, +5 Inherent, +2 racial: A Grey Elf with a starting Int of 16 can make this]
Lvl 39: Int 44, Multispell: 1 x Intensified, 4 x Quickened Intensified (2400hp)
And I'm not suggesting this build is optimized, either - it probably isn't. But I
would suggest:
1)
Vengeful Gaze of God should be available by about 40th level;
2) It should do about 600d6 of damage on a failed save. This is conservative.
I think that the versatility offered by the conventional caster's feat selection above (which extends far beyond
disintegrate) should not be paralleled by a narrow selection of feats focussed around the
destroy seed. That would be penalizing the epic caster too much. Using DDQ, two epic feats (one to increase damage to 4d6 per +1SP, and another to 8d6 per +1SP) could deliver a VGG-type effect at a USP of 71. It'd be nice to change it from a ray to a target (+4) (I think this factor is sound). That would leave 33 points of mitigation to find for a 39th-level caster: 17 points of backlash could do it for an Autoimmolator. As long as you make one of the prerequisites for the second feat 42 ranks in Spellcraft, it would work. (Edited, my math sucks)
Edit: The
ruin suite of spells becomes:
Ruin: deals 60d6 damage - USP 30: +16 (base) +4 (target) +10 (+20d6). Entry-level spell, with advantage over maximized
disintegrate of no ranged touch attack. 6 points backlash brings it within range of a 21st lvl character.
Greater Ruin: deals 120d6 damage, requires an epic feat w/30 ranks Spellcraft - USP 30: +16 (base) +4 (target) +10 (+40d6). 120d6 at 27th-level not too shabby. 10 points Backlash will net you another 40d6 (Autoimmolator 80d6). I think that whatever epic feat is required here, it should have a wider application than just 2d6 -> 4d6.
Vengeful Gaze of God: - as above. The prerequisite feat should be narrow in scope.
You're right about mitigating factors, though. Need to be careful with them.
Edit: I'm not sure how much the ranged touch attack requirement of
disintegrate should inform the progression of the
destroy seed - which can be changed to a straight targeted effect. I guess it depends on the deflection/luck/insight AC bonuses of the opposition. And rays can crit, of course. This might require some number crunching, but my gut feeling is that 600d6 at lvl 39 is OK.