my personal guide and recommendations for the Ratking boss fight for those interested and uninterested yet saw this. (just typed it here was to lazy for link stuff)

weapons: da loadout

Kendals (dualwield is basically required) any attachments that gives ammo and fire rate. (remember to buy the kendalls to pack them.), The FHR (u want get the epic rarity from the multiplayer clan missions at lvl 50 because it gives health almost every zombie kill. but don't want to because of the grind, fair enough, but the boss will be a bit harder.) also any attachment that do piercing/headshot damage, fire rate, and mobility. Also remember to grab any chi since you will only be using the ninja star on the Rat king during brain step.

(cards optional) explosive touch during the heart step, and twice the pain during the final Rat king shooting

perks: da perks

jug, bang bangs, quickies, and deadeye dewdrops(up an atoms if u want, but if you go down it may as well be a run ender)

pre steps: da steps (if ninjas spawn before the final Rat king spawn it's a run ender) :)

personally from my 12 hours of "solo" runs immediately look left while teleporting and you may be looking right at the rat king before the fight stops. (if more than one person you may have to remember where to look. (may be console only idk)

shoot the rat king until the first gong then go for heart or eye step first after the gong.

heart step: kill zombies on acid spots that spawn on the outer circle of the sewers get rid of all the spots until you hear a gong.

i say stand in the acid or in the center to get view of the whole room to kill zombies when they fall onto the acid spots. (epic FHR will help with the acid due to healing when you kill zombies) then shoot the zombies as they fall from the spawns to get rid of the acid spots. (I believe if they die in the air as they fall it counts as long as they are above the acid spots).

shoot rat king till gong

eye step: after putting the eye in the center symbols will spawn on the roof and maybe on the walls, shoot them till their gone and you here the gong.

try to loop the zombies by running around in the middle circle of the sewer while shooting the symbols, (where the water is). personally, try running and jumping while training. (also if using the dualwield kendals try shooting them one after another not at the same time to reduce chance of no-regs).

shoot rat king till gong sound

brain step: a brain will be placed in the middle, and a few zombies eyes will glow blue and try eat it while the rat king tries to stop them. (the ninja star will be used during this step on Rat king).

the first "brain eaters" don't matter, what matters most is that as soon as you place the heart try to go into chi mode and throw a ninja star at the rat king WHILE he is slamming his staff. if done correctly you will see a hit marker and the next Rat king spawn will show an animation and he will not use his staff either for the rest of the step. (or for like a min or 2) then loop zombies until the step ends by a sound of a gong. ( I personally kill a couple zombies that enter to thin the herd but it may raise difficulty of training.)

and finally shoot rat king till he disappears and the timer shows.

hint: you can go down during the timer phase as long as the Rat king has disappeared due to Pam being there.

was bored and made this, hope people see this and try a run . thx 4 reading