Digimon Adventure 02: Diablomon Strikes Back (2001)

Original title: デジモンアドベンチャー02 ディアボロモンの逆襲

In this movie, that takes place three months after MaloMyotismon's defeat, the DigiDestined go up against Diaboromon again. Tai and Matt head back to the Internet to deal with him with Omnimon, while the younger Chosen Children go to deal with the rampage of a swarm of Kuramon (Diaboromon's Fresh form). With the help of Angemon and Angewomon (with T.K. and Kari), Omnimon was able to destroy Diaboromon again, but it turned out to be a trap, as his destruction allowed many more Kuramon to go to the Real World. Things go out of control when the Kuramon in the Real World merge to create a Mega level called Armageddemon, an alternate Mega in Diaboromon's evolutionary line. It is so powerful that neither Omnimon nor Imperialdramon were able to defeat it on their own.