Hi, going to type out a mini-guide for the entirety of Sephirah's Meltdowns since
I couldn't find any others.

SPOILERS BELOW.

Tl:dr: The first 8 cycles are pretty easy. Just survive the first 4 (you can pretty easily go Artificer + grinding teeth with her stun to get food nearby with minimal effort) then kill a king vulture. Cycle 9 is when it gets hard.

An "Arbiter" spawns in every room you enter except for dens. Arbiter is a Guardian that you'd normally only encounter in Ascension endings. You kill it with spears and spears only to the head (no firebug spears). If you have homing shots they will NOT work and will make it harder. Every cycle you rest increases the speed and gravity of the world, but saves the damage dealt to the Arbiter. After that you will need to rest to 12 cycles, and if the Arbiter is defeated then, you get 30 food pips and win.

Tip for Arbiter: Going into Five Pebbles from the wall will make killing the Arbiter very easy. It can't spawn in more mobs, you will only be fighting the Arbiter. I would open the map every now and then to search for a golden "x" on it. You will need to hit this "x" with a spear to basically keep the Arbiter attackable. If there are any golden "x"s on map when the Arbiter hits 10%, it will become invincible, and if you are hit by any of its stunning attacks you will get killed by its spike attack. I also highly recommend trying to kill the Arbiter in 1 cycle, as the speed + gravity increase can make it almost impossible to check the map -> search for gold x -> dodge everything in the background. Again, if you kill the Arbiter in the room outside of 5P's puppet chambers, you'll be very safe and pretty much a free kill.