Batmo cave is full of... Batmos, there a few Chobin Hoods and Lime Slimes here as well. To get through go north-west, head round to the upper-left and pick up the chest containing an Angel Grail, then go north-west again. In this room there will be nothing until you reach a certain point, then three Lime Slimes appear and a Metaball will block your way back. Ignore the metaball for now. Your weapons will be useless against the slimes so press to change to the Heroine, hold down to unleash Wisp, then let it out and it will attack them. Head north-east.
In the next room there will be four Chobin Hood. Kill them all to receive a Bow. You can select the weapon by Pressing in the ring menu, this is a Jab weapon and can inflict damage on the Lime Slimes (from a distance.)
When you go south-east you will encounter another Metaball, this one is Jab so use your bow. Go right and jump up the ledge and open the chest for a Gundrop, then drop down and exit to the south-east.
This is the final room, it is suggested that you switch to the heroine and clobber the Lime Slime with Wisp (if you have enough MP), then go left and round with the Hero to clobber the Chobin hood with your sword. Switch to the bow and beat the Lime Slimes (or use Heroine's Wisp), then go down and kill the Chobin Hood. Go right to the Metaball, it is a bash this time, so switch to the Heroine and use the staff to kill it, then exit to the south-east.