Mirage is looking to help Rampart with creating some new gun hop-ups in exchange for a generous reward. However, Rampart doesn't make this easy for him, as she requires Mirage to bring back a special gem from a place he hasn't been to for a while: Dimension X45-D9A (Equestria). In order to obtain this, Mirage must acquire the help of Crypto, Wattson and Wraith in order to get a portal there and back, as well as make sure the data matches that of the gems they are looking for. After agreeing to split the money evenly, the four travel back to Equestria to locate and retrieve the gems. But along their journey, things don't exactly go as planned.
This takes place after Apex Legends - Season E, hence the reason the Legends are known throughout Equestria. However, no knowledge of the past story is required to understand this one.
This takes place just before Season 8 of Apex Legends.