Beelzemon is the Mega form of Impmon.
He has a humanoid demonic and biker form. In Blast Mode he has wings and a laser cannon attached to his arm.
Impmon was digivolved to Beelzemon by Caturamon in exchange for his mission to kill the tamers and their Digimon. He became the official rider of the evil motorcycle Behemoth, in control unlike its other riders. After driving by Calumon (who incidentally the Devas were trying to capture) he destroyed Infermon and absorbed his data, before Caturamon reminded him of his mission. Beelzemon confronted the tamers, threatening to kill Kyubimon before a storm caused by Juggernaut caused him to ride away.
Beelzemon later returned and attacked Takato, Henry, and Terriermon, who digivolved to Rapidmon. When the other tamers arrived, Kyubimon fought Beelzemon but was nearly killed until Leomon stopped him, punching him in the face and telling him that he was being used, and to have power is not to be strong. Beelzemon destroyed Leomon and absorbed his data. Enraged, Takato caused Guilmon to digivolve to an evil form, Megidramon.
Megidramon nearly killed Beelzemon, until Makuramon arrived and called Beelzemon pathetic, saying he was a pawn in a game he couldn't understand. Annoyed, Beelzemon destroyed Makuramon and absorbed his data, and when Rapidmon and Taomon tried to stop him, realizing what a threat he was, he used a variation of Makuramon's Primal Orb in an attempt to absorb them. Although Henry and Rika saved them, Beelzemon absorbed their Ultimate data. With the combined data of ultimate level "monkeyboy, rabbit's foot stew, and french fried fox tail", Beelzemon overpowered Megidramon. Completely insane with power, he declared his intent to absorb the Sovereign themselves.
Eventually Takato and Guilmon biomerged to Gallantmon, who gained the upper hand on Beelzemon and destroyed Behemoth. However, when Gallantmon destroyed Caturamon, Beelzemon absorbed his data and began to overpower Gallantmon, but with help from Guardromon Gallantmon defeated Beelzemon with Shield of the Just. Before Gallantmon could kill Beelzemon, Jeri told him not to, and Beelzemon left, regretting his actions.
After being attacked by some Chrysalimon, he dedigivolved to Impmon.
After returning to Earth and deciding to fight for good instead of evil, Impmon digivolved to Beelzemon, this time in Blast Mode, with wings and a laser gun attached to his arm. He helped WarGrowlmon, Rapidmon, and Taomon destroy the D-Reaper agent Pendulum Feet by severing the cord connecting it to the D-Reaper.
Later, Impmon digivolved to Beelzemon again to try to save Jeri from inside the D-Reaper's brain, but became trapped by its tentacles. He later got free and was confronted by an eyeball where the D-Reaper did a scan on him and reminded him that he tried to kill the tamers and destroyed Leomon. Beelzemon wasn't as affected as the D-Reaper had hoped, already viewing his actions as unforgivable, and fought the D-Reaper, which destroyed his laser gun (initially a toy gun given to him by Mako). After Gallantmon destroyed his shield, Beelzemon used Leomon's Fist of the Beast King (aided by the spirit of Leomon, briefly returning from the other side) to punch a hole in the D-Reaper's brain. However, seeing Leomon's attack come from his killer caused Jeri to freeze, and by the time she was willing to accept his help, the hole healed up, and Beelzemon was nearly killed by the D-Reaper's projectiles striking him in the back. However, thanks to Grani, he was not destroyed, but dedigivolved to Impmon.
- Double Impact - Shoots the enemy with his guns
- Darkness Claw - Slashes the enemy with his claw
- Corona Blaster - Shoots the enemy with his laser cannon
He also has wings in this form and can fly. Also, he can use the attacks of any Digimon whose data he absorbed, as he demonstrates with Makuramon and Leomon.
- Beelzemon is one of the only two digivolved forms whose voice changes, the other being Antylamon/Lopmon. Whenever Guilmon, Terriermon, Renamon, or Guardromon digivolve, their voices remain the same.
- When Gallantmon is about to kill Beelzemon, he says "Go ahead!" This happens several times in other media, always ending with the hero either choosing to spare the villain, or being talked out of it. Vegeta says it when Krillin is about to stab him in Dragonball Z, and Goku tells him not to. Steve says it when Darren is about to kill him in The Vampire's Assistant, but he decides not to. Teasle says it when Rambo is about to kill him in First Blood, but Trautman tells him not to.
- His name is derived from the name Beelzebub, which is sometimes used as a demon and sometimes used as another name for the devil.