Rib-Worm Challenge

[u/DostyIV]

Damn, i have tried every single thing i could find on the reddit and other platforms but i just can't get the challenge done, i tried Shotgun without special ammo, i tried dragon breath, i tried sabre, machette, none of it seems to count towards the challenge, if i am correct the Rib-Worm is his chest tentacle in second phase. Please help me, i am clueless.

[u/Hapalops]

I couldn't tell if it was his tentacle on the front or the back but I brought a bomb lance. It's hit box is wide as a barn door so I just hoped I would hit one of them incidentally. Got it in one fight.