This is the 1 controller each method. Slower but so much easier to set up.
Private (Custom Online) Arcade Deathmatch.
Bot difficulty... Beginner - Same running speed on all difficulties.
Rounds... 20 (750 kills/Assists) Rotate roles at start of round 11.
Round score... 75 (Kills)
Execution rules... off
DBNO... 6-7 (Gives you a chance to throw a fresh flame on them.)
Friendly fire... off
Make sure to LOCK the slots on your team so it's just you and no extra friendly bots.
The method is simple. BLOOD DRIVE! 1 person goes as Lizzie or Mac because they carry shock grenades. The other person goes as Kait as she carries Incendiary grenades. Work up to about 10 Skulls each hiding and gunning down the bots running in. If you die twice in a row without a kill or assist you get a skull anyway. Once you're both good on skulls. Throw a shock grenade as Lizzie or Mac at the most inner doorway of spawn covering the whole inside area of the 2 door ways then throw an Incendiary grenade as Kait at the doorway too. The bots will charge in the doorway to attack you but will get stunned and take damage from the shock grenade. They will go straight down and the Incendiary grenade will kill them. Resulting in Kait getting a kill and Lizzie or Mac getting an assist. Keep the throwing reasonably consistent but space out carefully so you don't run out of grenades. Once you hit 75 kills the round will end. Repeat over and over every round until you finish the match or rotate roles. Easy 750 kills or assists. Switch roles and do the same for another 10 rounds of 75 kills and you are both even. The best part about this method is your skulls carry over into the next round so you can start throwing immediately without having to fight for them. Each round should take 5-6 minutes. Each match of 10 rounds should be 1 hour long so 20 rounds should be 1 hour 50 mins - 2 hours. Keep away from view of the window and doorway, you will get shot through it. This is a great method for 2 people to work on together.
You can also work on kills and damage towards the 100,000,000 damage achievement by just playing as Lizzie or Mac throwing shock grenades solo. The bots keep getting downed if you cover the doorway. After their 3rd down they will die. This is great for grinding damage and kills but takes slightly longer than the method stated above. You can boost kills solo as Cole or Benjamin with flame pools they leave behind after each kill but this will not boost your damage as much as the shock grenade only method. Good luck and thanks to everyone who I boosted with to make this work.
Shout out to Sijore X51 & Groznia.