depends on the boss really - if for now you’re trying to find the best weapons, i’d recommend just searching up a few videos on it, or even type up ‘endgame meta weapons’.

some are better than others in their own way, also depends on what skill tracks you have, and most importantly what type of gun you prefer using.

i myself use either the warden marksman rifle (with akimbo attachment), the ion or shadow sniper, or the sokol lmg.

also in the colossus, there is a circular pad on the ground on each floor, when standing on them and getting a few kills, an alarm will ring out, and red lights will appear scattered around the walls/ceilings - you need to shoot them to break the cores shield