Urobolus is a giant snake that guards the Limestone Cave. It is first encountered just as the party is almost through the cave. Just before he appears, Lavitz notes that this is the guardian of the cave. Then Urobolus appears and the battle begins.
The Urobolus is an earth element snake. Its attacks can poison the party, so it is helpful to equip a character with a Poison Guard, preferably Shana. After a time, it will retreat into the rock and can only be hit by an arrow from Shana or a magic attack. Dart and Lavitz cannot hit him and therefore must Guard or use Attack Items. Urobolus will eventually come out of the rock so that Dart and Lavitz can attack again. With enough well-placed Additions and magic attacks, Urobolus will be defeated by a finishing move from Dart.