I'm yet to find a decisive guide on the Tek Cave and the Overseer literally anywhere online. I've gotten a bunch of contradicting information, so I have a few questions

Tek weaponry/armor - Can it be used in the Overseer fight?

Will I be able to get rexes through the Tek Cave and to the Overseer?

Is there anything I should be taking in other than rexes and ascendant armor/weaponry?

Anything else I should know?

I don't even know what the Overseer looks like, by the way. I have no idea about this fight, other than that it's quite difficult. If it's of any relevance, I'm playing with one friend on non-dedicated. We have 18 30khp 800%dmg rexes, a yuty and a pig, which has worked for all of he bosses so far.

So what should I take into the tek cave? That's all I'm asking for, help me out pls