Parasimon

Parasimon is a Mega Level Mutant Digimon.Its name derives from "parasite", an organism that lives by attaching itself to and feeding off of another.

Abilities
It can control others by connecting to their back and giving them supernatural strength to protect the Parasimon. However, when it takes control of someone, the one being possessed becomes "stuck" on their last thought. For example: Locomon was "stuck" on one line of a song he was singing when he became possessed: "I wanna run, and I'm gonna keep on a' runnin!" Rika was thinking of her father pushing her on a swing in her childhood. She was singing a playful little song; therefore she, in reality, as she was swinging a huge monkey wrench at Takato, she suddenly started to sing the song she sang so long ago.

Although Parasimon is a Mega Digimon he is very weak and can be easily defeated by Digimon on lower Digivolution stages. However in great numbers they can become a major threat.

Runaway Locomon
The spider-like Parasimon used his mind-controlling abilities to seize control of the train Digimon, Locomon, and sent him hurtling through Tokyo towards an opening rift between Earth and the Digital World at Ichigaya station. Using a camouflage ability to remain hidden, Parasimon sat atop Locomon, and observed as the Digimon Tamers attempted to stop Locomon‚Äôs progress. When Takato, Rika and Renamon boarded Locomon, Rika attempted to smash his furnace with a wrench, but Parasimon‚Äôs tendrils emerged from it and entwined her, enabling him to control her mind, as well. Using memories of her father and a song she used to sing with him to manipulate her, Parasimon had Rika attack Takato and Renamon, but when the conflict made it‚Äôs way to the roof of the carriage, Parasimon revealed himself.

Guilmon was able to free Rika by severing the tentacle holding her with his Rock Breaker, but after Locomon Digivolved into GranLocomon, Rika made an attempt to stop him from disconnect the carriage she was in, and was grabbed by more tentacles. Takato and Guilmon Biomerged into Gallantmon and severed the tentacles, then destroyed Parasimon. However, before he deleted completely, Parasimon sent a signal into the rift that summoned a massive swarm of other Parasimon to Earth. They began wreaking havoc in the city, and all the Tamers and their Digimon engaged them in battle, finding it easy to destroy the individuals, but nigh impossible to destroy the multitude, as they continued to pour through the rift. Even the arrival of Justimon and Beelzemon failed to sufficiently turn the tide, but then Gallantmon assumed his Crimson Mode, and flew into the heart of the rift, using his Final Justice attack to obliterate all the Parasimon in one shot.