A question came up in our recent game...do alchemists bombs damage Incorporeal creatures? Is the bomb damage considered magical?
The bombs are supernatural which makes them magical. That is all that is needed to harm supernatural creatures. It still only does half damage though.
Magical weapons and magic(not just spells) harm incorporeal creatures.
PRD, Incorporeal wrote:
Incorporeal (Ex) An incorporeal creature has no physical body. It can be harmed only by other incorporeal creatures, magic weapons or creatures that strike as magic weapons, and spells, spell-like abilities, or supernatural abilities. It is immune to all nonmagical attack forms. Even when hit by spells or magic weapons, it takes only half damage from a corporeal source (except for channel energy). Although it is not a magical attack, holy water can affect incorporeal undead. Corporeal spells and effects that do not cause damage only have a 50% chance of affecting an incorporeal creature. Force spells and effects, such as from a magic missile, affect an incorporeal creature normally.
PRD, magic wrote:
Supernatural Abilities: These can't be disrupted in combat and generally don't provoke attacks of opportunity. They aren't subject to spell resistance, counterspells, or dispel magic, and don't function in antimagic areas.