Gears 5

Not much of a guide, but didn't see much else written for it. Just got this tonight, and here's how I did it.

Firstly, I had two Xboxes. Doing it solo, I can't really help ya. But with two boxes, have the host box start a private horde match. Public horde might work for ya, but I don't like leaving things up to rando's if I can help it. Matchmaking Horde doesn't work either, as the highest difficulty goes to advanced, not Master.

On the hosting box, pick the character as Jack. This is cause he can go invisible and not be killed (as easily). I looked at all the maps, and they all had regeneration as a modifier, which lets the enemies regenerate health over time. The only one that didn't, was the daily featured map (for me it was Nexus, and other daily featured maps may have enemy health regeneration.)

Have the second box join, and also have them be Jack. I found the ability to hijack the boomshot scions to be pretty effective. They don't know you are taken over until you kill a enemy unit(most of the time anyway). Once your hijack is over, zap anything you feel like until you go down. Then have the second box return to main menu. Dashboarding works also, but just takes longer. Invite the second box back in from the host box, and just continue until you can whittle them away.

Got lucky on my run, as I had two Snatchers as the bosses, and lambent also spawned, so they fought each other till only a few were left to mop up.

Can confirm this achievement popped on both boxes, but as with all things Xbox, user experiences may vary.