Had a clan event last night of Giant Mole killing, and I decided to go for once.
The mole is so, so weak. In total, over the 90 minutes I was there, I got hit for about 30 damage total. The mole's high combat level (230) seems to be based almost entirely on defence, as it is hard to hit. I used a normal melee weapon and armour, with a spirit terrorbird + scrolls to keep energy up, as it is tiring chasing the mole everywhere.
It can easily be solo'd, and with the 8 of us that were there, it didn't last long, and most of the time was spent waiting for it's 2 minute spawn time. There is also a handy summmoning obelisk in the lair.
A covered light source (such as sapphire lantern) and a spade are needed.
They drop mole claws and mole skins, which can be traded to Wyson for bird's nests, but nests obtained this way seem to have lower rewards than normal ones.
It also has a chance of dropping higher level items, such as rune med / battleaxe, and dragon spear.