Lost Soul

Lost Souls are a type of enemy from the DOOM video game franchise. This demonic entity appears as a floating, horned skull enveloped in hellfire. It hovers through the air until it spots the player, at which point it will fly at high speed in the player's direction and explode upon impact.

DOOM (Classic series)
Appearing as early as the second stage of the first game, Lost Souls are typically found floating idly and quietly, with no flames surrounding them. They always appear in groups and usually with other demons nearby. When they notice the Doomguy approaching, they will suddenly ignite and will hiss loudly as they launch themselves towards the player. If they miss the player, they will keep moving in the same linear trajectory until they hit something, upon which they will explode.

In DOOM 64, Lost Souls are considerably tougher. They are also capable of stopping mid-flight and turning back to attack the player again at greater speed than before.

DOOM 3
In DOOM 3, Lost Souls look radically different than in other games. They appear to be severed, hairless human heads with sharp teeth, augmented with mechanical rocket engines that allow them to fly. The engines are responsible for the flames that surround the creatures.

Like in other games, Lost Souls move about in groups and will charge at the player when they approach. In some stages, they appear to be transparent. These demons are responsible for possessing humans and transforming them into zombies.

DOOM (Modern series)
Returning in DOOM (2016), the Lost Soul has a more stylized version of its original appearance. It resembles a demonic skull with long, gnarled horns and has evil yellow eyes. When idle, it is surrounded by blue flames that turn red when it spots the Doom Slayer. It attacks by launching itself at the player in a kamikaze run and explodes upon impact. If it misses the target, it will keep going until it hits something.

In DOOM Eternal, Lost Souls can not only be found floating around of their own volition, but are also used as projectiles by Pain Elementals.