Gold coop challenges
I know it's a pain to find a coop challenge partner since this game is so old. I've got them all done but if you're willing to do the leg/prep work I'll help you out. I.e. Get 12 boomsticks in your inventory and i'll join to help with the 5 boomstick challenges or get 12 super bfgs in your inventory and i'll join to help with the bfg challenges.
GT: FNSUITE GHOST