Guess what.

I wonder, how? And is the inability to hit him with a sword/spells/arrows/a glass club – a bug or a feature?

O_o I don't remember what I used to hit him with. I think it was a trophy sword, maybe even Umbra. And I threw a couple of fireballs for good measure. I was preparing for a tough battle, but he died after a couple of hits.

No.
The next person won't answer me until at least 12 PM Moscow time.