I wrote a guide about beating Legendary back when the Archives event ended and today Uprising is back in the Arcade, so I’m posting the guide here for those who may want to give the achievement a go.
google doc:
https://docs.google.com/document/d/1zvyyp3-11YlxyZLcJrsPquaXBrQ4rlfK5gwao4eKrYs/edit?usp=sharing
markdown:
https://gist.github.com/mecha-lynx/764605620f279a12c39d8f97b32302a6
They’re the same but I’m posting both links because some people might prefer one over the other. Keep in mind it takes coordination to get it done so you’ll probably need friends to do it or just try your luck with randoms. You should expect multiple tries even with a good group though. Should be at least some people trying it today.
Good luck!