With the Armored Spider, I think I mostly lost patience, but it seemed like a fight that could be managed with being persistent and memorizing the patterns.
But damn, Flamelurker! The worst thing about Flamelurker is, that it takes freaking forever to get there. If I would respawn right in front of the chamber, I wouldn't be worrying to much about it. But running 10 minutes through the maze to die within 30 seconds just isn't fun at all.

Now that I think of it, can it be that the five Greater Demons at the end of each world are actually the easiest bosses? Except for
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the very final boss. That one was just soo weird. I thought the maiden had betrayed me and wanted to feed me to him, but then there was just that thing in the puddle, and I shot it with 10 arrows and it was dead. Never tried any ranged attacks at me, nor did it move away from it's spot. Is it supposed to be basically the easiest enemy in the entire game?