The Imp is the first hell monster encountered in Doom. It is the most common monster in the game, along with Possessed Humans. They are small, brown, agile creatures with orange eyes, more similar to the typical idea of an Imp rather than the more humanoid versions from Classic and Doom 3. Imps are thought to be a lower form of the Summoner. The Imp doesn't get along with higher-ranking demons like Barons of Hell, Hell Knights or Mancubi, which often leads to random fighting in Hell. As a result, the evidence indicates that there is unfairness among the legions of Hell. They first appear in The UAC.
UAC Report File 388OAOYT
Imps, ferocious and agile demons, are found all over Hell and are often used in the front line during concerted attacks in either dimension. They revel in battle, feeding off their victims, when the hunger takes them.
UAC Report File 8WBD0DT
Despite their low status among the demon ranks and their seemingly endless numbers, Imps have unique characteristics in battle. Some prefer fighting from an elevated position, while others will rush their target and swipe at them with razor sharp claws. Walls and obstacles offer no defense against Imps as they will leap great heights and easily hand from surfaces. The Imp is capable of channeling Hell energy through its hands and shaping it into a projectile. As the Imp channels the energy, airborne particles and debris are sucked into the maelstrom to create a condensed, superheated fireball. The mechanics of the Imp's ranged attacks suggest that they are actually a lower form of the Summoner.
The Imp is a small and agile demon with a body type similar to that of a Summoner or Prowler. They have slim bodies with a brown and purple skin tone and large, bony spikes protruding from their backs similar to the original Doom. The Imp also bears orange glowing eyes.
Unlike the original Doom, Imps in the reboot are very agile, being able to grab onto poles and columns and move around at twice the speed of the player. Imps also throw their fireballs faster than they did in older Doom games. Occasionally, Imps will 'charge' their fireball, increasing its damage at the cost of a longer wind-up time.
An Imp that kills the player knocks the Doomguy to the floor, turns him over, rips his guts out, rips off his left arm and then uses it to smash his head in with one blow.
Imps can leap in nearly any direction, hang on pillars and walls, and run fast, all while still attacking the player without any pause. Amongst lower-tier enemies, they have already been described as "dangerous," with their fireballs doing significant damage, as much as 60 hit points in the game's Nightmare skill level. There is a brief wind-up to their fireball attack, giving barely enough time for the player to dodge if his attention is focused. A "harasser" unit by design, Imps will often retreat from the player and try to find purchase on a higher, more distant surface from which to attack. This is in contrast to the previous incarnations of the monster, which always sought to close to melee range - this Imp rarely resorts to melee attacks unless the player chooses to close to that range. It will occasionally leap toward the player to strike if it is at medium range, however.
Imps underwent a dramatic redesign between the E3 2015 initial public presentation of the game and the final release product. The earlier design was closer in appearance to a smaller version of the Hell Knight, suggesting some kind of relationship between the two. The final Imp design added distinct features to the head and body, two prominent glowing eyes, and accents of purple color which seem to call back to the Nightmare Imp seen in Doom 64.