I think its pretty obvious as to how to start on your journey to become a Rat King, you pick The King of Progress since he's the guy with the rats.


Now this does require certain perks to work from his kit, so you cant use this immediately, but after a run or two (depending on how far you get) you should be able to use these perks. Additionally, I will be explaining these as to how they activate/work together, using this numbering system as a structure to label them.

[ 1 ] [ 2 ] [ 3 ]
[ 4 ] [ 5 ] [ 6 ]
[ 7 ] [ 8 ] [ 9 ]


1,7,9 - All are troop bonuses for stats, not very important so feel free to swap them out if you want to.

2,3,5 - These are mainly meant to increase the multiplier of the Progress specific perks towards the bottom, this was the best orientation I found, so I would recommend it.

4 - This gives all troops an innate 40% crit chance.

6 - This makes it so that all rats will automatically level up 4 times every time one is placed.

8 - This makes it so that every single level up gives you +4 gold to have a good source of economy so that you can ball out at shops early game.

Starting out - As per usual, set your Base far back, it doesn't particularly matter which specific plot, since all of them will be filled with rats anyways. As for the cards, the IDEAL start is something similar to this:

Since it has at least one rat, and the converter can be helpful when taking care of some of the more difficult early enemies.

Early Game - This entire strategy is heavily RNG based, because some of the best cards you can possibly think about getting are Offering (Spells), Earthworks (Stone), Overhaul (Progress), and Clone (Nature). If the game just decides otherwise, you get no rats, therefore no money, because no constant level ups, and trust me, every game needs a solid economy to get the most out of each run. I would recommend just trying to survive first before getting the Rat Engine™ up and running. Another early game fantastic choice is Reinforce on the first rat you place down, meaning every time a level up occurs it gains +1% damage, considering this is the first rat of the game, and these can level up infinitely, they're pretty useful.

Offering is a recommended choice if you like to gamble, that is why I pick it.
Earthworks allows us to very early on open up more spaces for the rats to spread.
Overhaul can really snowball after getting a large amount of rats.
Clone is just a free rat to place down so whats not to love?

As an example, on King 2 difficulty, year 6, this is what my top Rat was at stat wise:

Mid/Late Game - If you have done this correctly, you should have ~1000 or so rats by year 15. Congratulations, you now have strong enough rats to overpower the entire game. Just keep removing them with Overhaul or Earthworks/Offering if possible to get even more, keep deleting the newest/weakest rat, and just get more level ups / rats from those sources.

Another example to show just how powerful rats can really be:






























Endgame/Endless - Other than that there really isn't a whole lot else to do, just keep spamming 'em. If you keep it up eventually your screen will look like this constantly:


And you WILL crash the game, its not meant to handle this many entities, and it will often break. The game engine itself cannot handle the sheer volume of rodents.