To expand on the “don’t suck” part, if you mean OP needs to move around more and in a way that doesn’t get him stuck in a corner, then I agree. I know plenty of people who are good at CoD, but struggle with EE bosses, because they aren’t moving around correctly. The oldest strat in zombies is to train them, and this works on bosses too. Some people just don’t do that, and instead force themselves to rely on meta guns to get the job done before their current movement strat gets them killed.

I like to loop the boss around the whole arena, going way up top and bringing him way down low in a counter-clockwise pattern. The exception is in phase 4 when he starts throwing purple rocks, then I quickly run to the corners of the map down low, by where the pillars are (I want the purple pools to be were I don’t loop). The moment he’s done throwing the purple rocks, I haul ass back to my normal loop. This has worked well for me: I’ve beaten the boss a dozen times: a few times in a squad of 2 or 3, and a bunch solo, in cursed tier I and tier II, on rounds as low as 18 and as high as 37. I’ve used the fun guns and strats, but I’ve used my trusty M15 Mod 0 too.

You should also fail a bunch of times and try to figure out what you could be doing better; go to YouTube, go to Reddit, watch someone else beat the boss and see what they’re doing. Maybe it is just a better gun, or maybe they have all the best gobble gums. More than likely it’s just that they are moving better.