Lost Soul/Resurrection of Evil

The Forgotten One's form is an echo of the original Lost Soul's shape in the previous Doom games, rather than its interpretation in Doom 3. It is a flying skull with two demon horns, and floats with a stream of flame behind it. Its only attack consists of flying towards its enemy and biting. It replaces the Doom 3 incarnation of the Lost Soul in the expansion pack.

Tactical Analysis
Due to the lack of melee weaponry, these enemies are much more difficult to eliminate from the original. As in Doom 3, the use of the chainsaw or weak weaponry can result in immediate death, however this incarnation has the potential to withstand a standard shotgun blast from midrange. On the other hand, the player has a new advantage over them; they can be caught by the Ionized Plasma Levitator (aka the Grabber). Once grabbed, they can still potentially fight the beam and hurt you, so it is best to immediately shoot them away, which disintegrates them.

Trivia
The name "Forgotten One" may be derived from the fact that Doom 3's Lost Soul has a new appearance. The shape of the Forgotten One, and thus the original Lost Soul, was "Forgotten", so to say.