This is the most difficult Battle Chest mode in the game due to a couple of reasons:
The teammate AI is severely dumbed-down and will often try to sprint towards the enemy recklessly without even trying to use their abilities.
The enemy AI, on the other hand, is greatly buffed and tends to abuse their abilities. For example, the All-Star will often use the Dummy Shield ability once they reach 75% health or below, making vanquishes difficult to perform;
The enemy AI also receives a massive damage and accuracy buff, so trying to take out the enemies in the open is guaranteed to be fatal.
They tend to stay grouped whereas your teammates will just wander on their own, which is the reason why the enemies can score vanquishes so quickly.
Because of these, it is strongly recommended that you attempt this Battle Chest with at least three people, as it helps getting rid of the dumbed-down AI teammates. Beating this in solo is apparently possible, albeit extremely difficult, due to the aforementioned reasons.
A decent character to beat this in solo is the Citron leveled up to the Master rank. Equip the Pulp Powered and Juiced upgrades, and take a lot of cover. Because the Citron's weapon is significantly offset to the right, this allows you to fire while taking cover. Taking out All-Stars as soon as you see them is a number one priority, as their attacks are very powerful, they can can deploy a Dummy Shield, and take a lot of hits to defeat, followed by Engineers due to their Bullhorn Swarm and Heavy Helper abilities. Use the EMPeach, take some cover, and eliminate them quickly before the stun effect ends.
Try to follow a Sunflower to gain some overhealth and regenerate your HP when you get hit. This allows you to last longer in the middle of a firefight.
The Navel Laser is very useful due to the tendency for the enemies to regroup. As soon as you see hordes of zombies, quickly take cover to the right side of an object, pull your Navel Laser, and fire it against them. The mix of Pulp Powered and Juiced will allow you to take them out very quickly and ensures that you don't run out of Navel Laser time before they're all dead. You can also use the Navel Laser when there are only one or two enemies if you're low on health or they're too dangerous to take out with the Juice Cannon.
