See Invisibility:
In 3.0 and NWN1/2 it lasts 1 minute per level. This makes it a sucky version of blindsight. No one ever casts it. In 3.5 it lasts 10 minutes per level. I believe this spell was simply not touched from NWN1 and we should change it to match 3.5.
Combust in 3.5:
COMBUST
Evocation [Fire]
Level: Sorcerer/wizard 2
Components: V, S, M
Casting Time: 1 standard action
Range: Touch Target: Touched creature or combustible object that weighs no more than 25 lb./level
Duration: Instantaneous; see text
Saving Throw: Reflex partial
Spell Resistance: Yes
You rub the oil against the flint and murmur the ancient words, touching your target. It immediately smolders and then bursts into bright flames.
This spell makes a combustible object or a creature’s combustible equipment burst into flame, even if damp.
If the target is a creature, the initial eruption of flame causes 1d8 points of fire damage per caster level (maximum 10d8) with no saving throw. Further, the creature must make a DC 15 Reflex save or catch fire (DMG 303).
If the target is a combustible, unattended object, the initial eruption of flame deals fire damage to the object as noted above. The object catches fire and takes 1d6 points of fire damage each round until consumed or someone puts out the fire.
Material Component: A drop of oil and a piece of flint.
Combust in NWN2:Catching On Fire
Characters exposed to burning oil, bonfires, and noninstantaneous magic fires might find their clothes, hair, or equipment on fire. Spells with an instantaneous duration don’t normally set a character on fire, since the heat and flame from these come and go in a flash.
Characters at risk of catching fire are allowed a DC 15 Reflex save to avoid this fate. If a character’s clothes or hair catch fire, he takes 1d6 points of damage immediately. In each subsequent round, the burning character must make another Reflex saving throw. Failure means he takes another 1d6 points of damage that round. Success means that the fire has gone out. (That is, once he succeeds on his saving throw, he’s no longer on fire.)
A character on fire may automatically extinguish the flames by jumping into enough water to douse himself. If no body of water is at hand, rolling on the ground or smothering the fire with cloaks or the like permits the character another save with a +4 bonus.
Those unlucky enough to have their clothes or equipment catch fire must make DC 15 Reflex saves for each item. Flammable items that fail take the same amount of damage as the character.
Combust vs. Scorching Ray, average damage by caster level:Combust causes flames to erupt around the touched creature, initially causing fire damage in the amount of 2d6 + 1 per caster level points, to a maximum of +10 points, with no saving throw. Each round after the casting the target must succeed at a reflex saving throw or take an additional 1d6 points of damage. This continues until the reflex saving throw is successful.
03: 13.5, 14
04: 18.0, 14
05: 22.5, 14
06: 27.0, 14
07: 31.5, 28
08: 36.0, 28
09: 40.5, 28
10: 45.0, 28
11: 45.0, 42
3.5 combust offers a significant increase in damage over scorching ray. The drawbacks are of course that it is a melee-range spell, and in NWN2 this generally means an attack of opportunity is granted on the caster. It also cannot damage multiple targets as scorching rays can. Also note that without weapon finesse, melee touch attacks use the caster's STR modifier, so most mages will typically have an easier time hitting with a ranged touch attack (I can extrapolate out the average damage per level of a mage with a STR of 10 and a DEX of 14 if anyone cares).
Average damage with no misses:
03: 13.5, 14
04: 18.0, 14
05: 22.5, 14
06: 27.0, 14
07: 31.5, 28
08: 36.0, 28
09: 40.5, 28
10: 45.0, 28
11: 45.0, 42
Edit: went ahead and did it:
Average damage adjusted for misses:
Assuming straight wiz/sorc, STR 10, DEX 14 against a touch AC of 12.
03: 06.75, 08.40
04: 09.90, 09.10
05: 12.38, 09.10
06: 16.20, 09.80
07: 18.90, 19.60
08: 23.40, 21.00
09: 26.33, 21.00
10: 31.50, 22.40
11: 31.50, 33.60
Since we cannot simulate all the things a creature can do to put itself out if caught on fire, and the spell already seems pretty damn powerful, I'd like to leave out the "catches you on fire" portion of the spell.
Any build with Weapon Finesse and some ability to tank would see a rather large benefit from casting Combust over Scorching Ray. But then second-level spell slots are typically very precious for these builds (being mirror image's level). At high levels, without the ability to catch targets on fire or sneak attack via flanking, scorching ray is clearly superior.