Within the 6 Month's after Cozy Glow was saved by the Paw Patrol, Twilight and their friends have assembled a team of heroes from throughout the multiverse. However, they're also gonna face enemies from throughout the universe.

If you want to know how the Main 6 know certain characters, then read these stories by other amazing authors first.
Avengers: https://www.fimfiction.net/story/285450/a-beautiful-new-age
Sonic: https://www.fimfiction.net/story/13892/sonic-generations-friendship-is-timeless
FNAF: https://www.fimfiction.net/story/228043/five-nights-at-freddys-mlp-style
Mortal Kombat: https://www.fimfiction.net/story/433161/mortal-kombat-defenders-of-equestria