Throwdows: Black Hoodie / Team Up, Throw Down Mission

Probably more of a free-play game if your not able to get it done before the  the intros are re-designed or decides all together than you can skip the intro missions to allow for people to not have all the game breaking happening.

Actually though, even if you get someone to join currently and they leave even in the event: it should still count but if it really came down to it you could create a second account and join your own event through cross-play if you have access to two consoles.