From Ardrana

Phantoms are images left behind by particularly strong death traumas. A phantom is like a three-dimensional movie image filmed at the time of death, in the place where it died.

The standard phantom may appear as almost anything. It often appears as the character who experienced the trauma -- a transparent image re-enacting the death scene. Alternatively, it could represent whatever was foremost in the victim's mind at the time of death; an attacker, or some goal left unachieved. Phantoms are experienced in faded colors, by all senses. Phantoms are often mistaken for ghosts, haunts, or groaning spirits, but they can not be turned as undead. Only a priest spell remove curse can dispel a phantom.

It is difficult to fight phantoms, since they are merely images and have no power to directly cause harm. They cannot themselves be harmed. Swinging weapons or casting spells into the area of the image does not interfere with the projection, and they cannot be reasoned with.

Although a phantom cannot directly do any actual harm, it is the very essence of magic and calls up a superstitious awe in anyone who sees one. The enchantment is such that the phantom affects both the mind and the senses of the observer. Creatures without minds are immune to the effects of phantoms, as are those rare beings who are somehow unable to experience them. Characters witnessing a phantom often panic and run away, or in the case of particularly vivid phantoms may even die from fright.

There are nonstandard types of phantoms that affect only one of the senses. Often, these are purely visual images, but they can also manifest themselves as sounds or smells. Of greater concern, however, is that there are some phantoms that are actually evil, created when powerful evil creatures from other planes are forced to return to their home planes. These phantoms appear at the will of the evil creature, and can seriously misinform or endanger any character it meets.

Note: Phantoms originally appeared in this form in the 2nd Edition Monstrous Manual for the AD&D game from TSR. Their use here is for the purposes of providing context for the campaign only.