I’ve cleared all of the depth 4 Chalice Dungeons with my sanity intact—barely. The Watchdog of the Old Lords, boss of Defiled Pthumeru layer 2, is quite possibly the most difficult boss battle I have ever encountered. It’s right there with Ornstein and Smough from Dark Souls and Maneater from Demon’s Souls.
It’s always worth it though. The feeling of satisfaction after defeating an insanely hard boss always outweighs the frustration of dying again and again and again.
Here’s the video of my battle with Watchdog. It’s quite boring, especially towards the end, and it doesn’t really convey how hard the fight is. Basically, your one slight mistake away from death the entire time.
All I have left to do now are the depth 5 Chalice Dungeons. May the Good Blood guide my way.