Galactic Commander Neptune

Galactic Commander Neptune was a high ranking member of Team Galactic who Tagg fought in Sinnoh at the age of 17 in a curb-stomp battle on his end. Enraged at his defeat by a child, Neptune spent three years in prison before breaking out in the time period between the Unova arc and the Ranger arc. Tagg first learnt of his escape after he managed to send him a letter promising revenge on not only him but everyone else he associated with, though he kept this fact away from the others for quite some time.. To that end, he used a Time Flute to lure Celebi close by, captured her, and managed to transform her into a Shadow Pokemon. After breaking Cyrus out of the Distortion World, together they created the new universe where the J-Team hadn't met up, with Neptune staying within Sinnoh post-Distortion.

When Tagg and his Pokemon showed up in Sinnoh to stop him, having used Cobalt to pinpoint his location, Neptune hid behind a barrier before having a multitude of enemies attack the party. Once that failed, he ran into a dimensional rift, Tagg and his main Sinnoh team following behind. After a climatic battle, Neptune ended up being sealed within the rift, Tagg deciding to let the legendaries decide his fate. Post-AU, he is currently stuck in a Cyrus-esque infinite time loop dancing the Carameldansen for all eternity.