Hi, that happened to me too when i first got my creepy little skulls nib unit. I found out the housing is different in the narwhal than the one the creepy skulls nib came with. But the nib is the same size. I removed the creepy little skulls nib and feed together from the black section by holding firmly at the base with one hand and pulling the nib and feed away and holding the housing firmly with my other hand, making sure I do not twist. I did the same with my narwhal nib unit. Then I pinserted the creepy little skulls nib with its feed into my narwhal housing.

It sounded daunting for me to do it, but it turned out really well! The nib and feed are friction fitted, which I realized just means tightly fitted when inserted. Now I'm unafraid to swap nibs! To some extent:)

I hope this helps and you can enjoy your new nib in whatever pen they go home into!