Step 1: Head to the rock formation at the back of the island as Mothra Larva.
Step 2: Get as close to the mountain side as possible, transform, and continuously jump while transforming. If done correctly, Mothra Imago will leap upon emerging, and you can gain access over the rocks.
Step 3: Just make sure not to accidentally run back into the Island mainland while exploring, or you'll have to start all over again!
P1 - Bigyoshifan223 P2 - nifanatic
No copyright infringement intended. GODZILLA and related characters property of TOHO. Footage and music are used solely for the entertainment of others, and to bring awareness to the franchise.