Digimon World Dusk: InsectPlant Quest: Drimogemon the Digger.

Talk to Lillymon and go find Tentomon in Dark Square. He will tell you to stop Drimogemon from digging in Login Mountain. Hit there!

So, go to southwest. Go up the slide to the northeast. Walk the path to the left and you will see a Drimogemon there. Talk to him and he will attack you.

Drimogemon 
HP: 1400~
EXP: 155 Beast
Bit: 100 bits.
Now you have to find the other two Drimogemon(s).

Go back to the previous screen on the top right to the southwest, climb down the ladder and there is another Drimogemon. Talk to him and repeat the same tactic to defeat him.

Next, go back to the northwest and climb up the ladder and go to right. Walk the path to the right, ignore ladder and you will find the last Drimogemon. Defeat him and return to the city. Talk to Tentomon and get your reward -- 145 Tamer Points, 6586 bits and a Sleep Core a.

*After this quest, you can find Drimogemon in Login Mountain.