I have a similar experience with Quakeโs final boss. Itโs the only thing in the entire game you donโt kill by shooting. Took me 3 freaking days to figure it out.
Itโs stupid as hell because itโs like the easiest thing to do, but no game had anything remotely like that, and it wasnโt a mechanic shown to the player at all in SP (if you donโt know you have to telefrag the boss by jumping into a gate when a purple spikey thing flying around the room clips through the boss).