**UPDATE** With the latest update, you should be able to search for my file share and download the map!
To find other players in MCC, select your name in the Roster, then select "Find Player" to access their file share, etc.
I have set up a Forge map you can load up in custom games and shared it in my file share. It's titled "Assists" and I'll give you a brief explanation of what to do!
The map is set up to accommodate up to 16 players, with up to 3 people gaining assists.
1. Set the map settings to normal Slayer, make sure to turn all respawn times to instant, score limit to unlimited, time limit to unlimited(thanks Rey27), and turn up player shields to 4x so the turrets don't kill the spawning victims too soon.
2. Bring in as many extra controllers as you can!
3. Choose who is getting assists, and have them get on the higher turrets(up to 3 people). Aim the turrets around the head of the spawning victims.
4. Choose one controller/person to get on the lower turret and have them aim a little bit below the spawn points so that this turret at least nicks all the falling victims before they teleport to death.
5. Turn off aim assist by switching to classic(thanks bvrgvndy), rubberband all shooting controllers if you like, and run all victims into the death zones to start the assist sprees.
If you need clarification, please ask!
Here's a visual aid:
Note: the kill turrets don't actually kill, they just get credit for the last bit of damage done.