The little alcove where the BFG is placed is marked as a secret, but since Doomguy can't reach that elevation (and since there is no Pain Elemental on this map to glitch into the sector), the secret is completely inaccessible. There are no other secrets, so the only criterion for UV-Max is 100% kills.

Right off the bat, this attempt was incredibly lucky. When jumping both to and from the Revenant ledge with the BFG, I didn't wake the Cacodemon or the Mancubus; this is one of only 2 times this has ever happened to me. The end was also pretty lucky as I Hail-Mary'd some plasma down a hallway in hopes of it killing an imp, which apparently it did. I also rushed the last room and somehow killed everything.