Caliban's Keeper is the first stage of IT Catacombs. Up to 3 R. Osts will appear here. To make it worse, the fish with freeze ability in point blank range, Henry is also here. Henry makes the traditional way to encounter R. Ost by using ranged Cats with meatshields more annoying.
- Snache, Croco and Squire Rel respawn infinitely every 6.7~13.3 seconds200~400f
- 1 R. Ost apepars at 50 seconds mark.
- When Base HP is 99%, it will spawn Henry and 1 R. Ost. The third and last R. Ost will appear 66.7 seconds2000f after the second one.
This is a stage broken by Gothic Mitama. She can permaslow the R.osts and resist the freeze from Henry.
Strategy 1: Uber-less line up
- Manic Mohawk Cat, Eraser Cat, Manic Eraser Cat, Macho Legs Cat, Manic Macho Legs Cat, Maglev Cat, Manic Island Cat, King Dragon Cat, Awakened Bahamut and Ururun Cat.
- Demonstrated video: 
Strategy 2: Vendor Cat and Kitten + Glass Cat
Row 1: Detective Vigler, Riceball Cat (Cheating Hearts Research Up M), Vendor Cat and Kitten, M. King Dragon, M. Macho Legs
Row 2: Glass Cat, Kasa Jizo, M. Eraser, Eraser, M. Macho Cat
It is fully possible to switch out the combo and damage cats for some alternatives, though I would not switch out M. Macho Legs as the wave attack is huge for clearing peons and hitting Henry behind R. Ost. The core here is to stall with 3 (maybe 4 if you do not use a Research Up combo) meatshields, stack a few Vendor Cats, and stack several ranged DPS. Once the boss wave is triggered the Vendor Cat stack can actually stun lock Henry while also stopping R. Ost from destroying your initial DPS cats stack. Glass cat should be constantly spammed once the boss wave is triggered. Put some effort into timing glass cat so it will hit R. Ost. With luck you will actually kill Henry before the 2nd R. Ost, at which point all you have to do is deal with at worst 2 stacked R. Osts when the 3rd and final one spawns.