Alternate Universes Collide is a story mission in South Park: The Fractured But Whole.
Plot details follow.
Head to the right from your house to get to Kyle's.
Note: Take a detour to Stan's house on the way. Randy is outside in front. Talk to him to start the side quest A Randy Mystery. Head inside Stan's house to find an Antidote Recipe in the kitchen. With this, there should be a new Crafting App on your phone. You can also find Toolshed's Character Sheet inside Stan's Room, and C-Cup Headwear in the master bedroom.
Defeat Alternate Human Kite
The Human Kite 2 from an Alternate Universe is an annoying cheater who will inject new rules during the fight (e.g. Taking an extra turn, restoring full health). Do your best and you'll come out ahead with little to no issue.
After a few turns, the Alternate Human Kite will attempt a special attack, only to fall off from Kyle's bed and knocking him out, resulting in the New Kid effectively "defeating" Alternate Human Kite. After which, Human Kite will become a Combat Buddy and ally. Don't forget to take a selfie with him before you leave, and loot the rest of the house upstairs and use the toilet.