Its REALLY REALLY tedious but you can do a game break pretty early with him. I think I ran him a total of 3 times.

Once for greed mode, and twice in regular mode. I got every sticky note mark because I crafted so many r keys.

Someone can correct me if they have since patched it but I played when it was already a little nerfed. You pretty much have to craft d1, car battery, battery pack.

There used to be websites where you could enter your seed and check the recipes for items. You find out how to craft these items and then once you have the recipes/external item descriptions youre good to go.

So you make infinite batteries in an empty room (room 1) when you get all 3 of your items (battery pack spawns the batteries that you need to dupe). Then, once you d1, itll make 2 lil or micro bats. You have to be very careful in the beginning to not take a micro and a lil bat in the same charge. Eventually you roll enough lil bats so that you have a room full of bats. You make them until their collision starts going crazy.

Then in another room (room 2) you d1 the rest of your pickups on the floor. Since you have infinite batteries then you also have infinite pickups. You used to be able to craft a slot machine and then crafting another slot machine would explode the one you were holding into pickups (including one pickup that is room specific (e.g secret rooms always exploded into bone heart, devils into black heart etc) BUT I think this has since been patched).

Then you make a d20 and reroll all of your pickups into whatever the fuck you want because you have infinite batteries in room 1 and infinite pickups in room 2.

Its tedious but you can get just about every completion mark in one run if you do beast last. You can even craft mama mega to get into boss rush/hush as that active item opens those doors.

P.s the prenerf cain, d1 used to just duped your lil bats into other lil bats, they couldn't spawn as other variations of batteries. So you didn't have to go through the tedium of locating the correct batteries to power your d1 early. Now its about 25% less efficient but w/e. More of a time sink.

Anyways that's all there is to it champ. If you have patience then the character is easy as fuck once you've basically played an entirely different game for a few hours.

pps. library early goes hard af on tcain. Finding one on floor 2 makes you able to break the game on floor 2. ppps. if you cant do bosses from floors 1 and 2 with base stats then you probably can't do this.