The Mud Ponbabar is the creature that Jack Russell defeats at the end of the Theater Vancoor mission, "Creatures of the Sewer".
The Mud Ponbabar is level 31
It is suggested you buy some Cure Drops, Mint Drops, and Flexibility Lotion. The Mud Ponbabar has an attack that can confuse, poison, and petrify you.
You can bring someone(s) along who can cure status ailments such as Flora or Romaria.
After you defeat him, you should acquire a Rune Saber and a Luck Berry as your loot. You also get 5000 Dagols as a reward for completing the "Creatures of the Sewer" mission.