In our D&D 3.5 campaign, for years, we have followed the rule provided in the Monster Manual 1 on the incorporeal subtype. Summarizing: corporeals that hit an incorporeal have a 50% chance to miss, whereas incorporeals do not have any miss chance when hitting corporeals (as there is no mention of this in the description of the incorporeal subtype).
This is in line with an answer given to a previous question from 2012: Are ghost touch weapons the only way to bypass the 50% chance to ignore damage against or by incorporeal creatures?
Of course, players in our campaign have followed the same rules, as they could go incorporeal with spells or their prestige class features.
Nonetheless, I have recently found the spell ghostform (Spell Compendium, page 103), whose description mentions that incorporeals have a 50% miss chance when hitting corporeals:
Your attacks while in ghostform pass through (ignore) natural armor, armor, and shields, although deflection bonuses and force effects (such as mage armor) work normally against you. Nonmagical attacks you make with a melee weapon have no effect on corporeal targets, and any melee attack you make with a magic weapon against a corporeal target has a 50% miss chance, except for attacks you make with a ghost touch weapon, which are made normally (no miss chance). Spells you cast while in ghostform affect corporeal targets normally, including spells that require you to make an attack roll (such as rays or melee touch spells).
Do characters that become incorporeal (in any sort of way, e.g. spell, class feature, etc.) have a 50% miss chance when trying to hit a corporeal creature? What's the general rule?
