Okay. Over the course of my time playing this game, I've discovered a combo that legitimately cannot die, can be AFKed, and will usually oneshot the NG+5 bosses. It works best on NG+5 but with some sacrifices can work on any difficulty, and it can be used to beat the entire game in a single run.

UNITS:
-Jester (Vital)
-Scout (Vital)
-Thief
-Spellblade
-Assassin
-Dual Gunner
-Merchant
-Usurer
-Squire (Vital)
-Chronomancer (Vital)
-Silencer
-Infestor (Vital)

ITEMS:
-Reinforce
-Ballista (Vital)
-Ultimatum (Vital)
-Vulnerability (Can be swapped with Critical Strike)
-Malediction (Vital)
-Meat Shield (Vital)
-Flying Daggers (Vital)
-Infesting Strike (Vital)

To play this right, you need to get a T3 Scout up as soon as possible. Scout/Squire start is the best for this. Make sure to get a Merchant relatively soon. You then want to get a T3 Jester up as soon as possible. This essentially wins every fight and gets you enough money to complete the set.

The way this works is simple. The maxed rogues all have chaining projectiles, and each chain does extra damage. This one-shots large groups of enemies, and the L3 Thief ability can kill bosses easily. Maxed Cursers is also vital, since you will be relying on the critters spawned by the Infestor and Infesting Strike to block Ice Bomb projectiles.

It's hilariously overpowered, I highly recommend you try this out. It will win you the game in a single run if you loop continuously.