When you get to the island where you are stuck and you get your bomb partner..

You need to use your bomb partners skill.

You have to do all the stuff with flavio and he lets you use his red skull and you put it in and you butslam 3 times on the red and use the hammer 4 times on the blue one. Then you throw the bomb guy on the skull stone and it blows up and then you go in.

You don't get a bomb thing to open it. Here is how to get in the cave. Observe the skull-shaped rock formation, and there will be a hole in the skull's left eye. Your partner will tell you that it is the shape of the Skull Gem that Flavio has.

So, go back to camp and tell Flavio all about it. Everyone will vote to let you take Flavio to show him the rock. When he sees the hole, he'll walk away a few steps away. Talk to him and he'll sing a song. Listen closely to his song, he'll say some things you'll have to do. If you don't understand, first insert the gem into the hole. Then the mustache stones will activate. Do three Spin Jumps on the red stone, and hammer the blue one four times. A platform will appear over the skull.

Throw Bobbery on the platform, and then he'll explode. The entrance to the cave will appear. When your in the cave, you'll hear ghostly voices along the way. Keep your HP max level high, and have health items ready, because I almost died without health items, but I guarded myself and had one heart point left.