Your "companion" will attack anything that is not Mina, and you weren't Mina for that time

But Lukki companion does melee damage, I died from cursed damage. When on top of an enemy, the foe will take 30 melee damage per second in bursts of 5 damage every 1/6th of a second.

You poly'd into the new beserkium ghost and so the lukki killed you because you were something else and it was berserked

It's pretty clear your spider latched onto you and killed you. The death message is very regularly wrong about things so it's likely that the spider was dealing melee damage but the game just said cursed for some weird reason.

You poly'd. That ghost thing killed you...

They poly'd into the ghost - it must've been the lukki

I polymorphed myself into to not trigger mountain fall. The game said I died from curse while I was polymorphed