Just beat it myself, got the third ending. Took my time before the battle, though, wiped out all the optional bosses I could find, (pretty sure I got all of them outright, @_@ ) even made sure to get the full-level Moon rune from that giant eyeball monster in the pit, because I AM NEVER GOING IN THAT PIT WITH THAT FREAK AGAIN. ._.
Yeah, the hunter boss Gehrman was a nightmare to fight. So powerful, so fast, and that Scythe (WHICH IS NOW MINE MWAHAHAHAHA) had some painful range to it. Taking him out with my (smaller) holy blade kept turning into this dance of dodgedodgedodgedodgedodgestrikedodgedodgedodgedodge. Beat him on attempt five, literally screamed "**** YEAH!" when he finally fell, despite the fact that it's three in the morning and I might have woken up the entire house. xP
Secret boss was almost laughably easy by comparison. o.o
Zanten, Doer Of The Things
Unless He Forgets In Which Case Zanten, Forgetter Of The Things
Or He Procrascinates, In Which Case Zanten, Doer Of The Things Later
Or It Involves Moving Furniture, in Which Case Zanten, F*** You.