He doesn't finish his cave in Ruby. That only takes place in Emerald.
I don't think you can, in emerald you need the nationaldex and POW! it's open but in ruby and sapphire you can't.
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In Pokemon Ruby, Sapphire, and Emerald, the Fossil Maniac is in Fallarbor town. His house has a large hole on the inside. When you go through the hole, he is all the way in the back of his homeade cave. NOTE: You get dig in this house. Talk the the Fossil Maniac's son before going into the Fossil Maniac's cave.
You can get ditto in Pokemon ruby by beating the Pokemon league then going to the cave the fossil maniac is digging he will be finished digging and he will say to be careful that there are Pokemon in there the Pokemon in there are ditto.
West of Fallarbor Town
The claw fossle is better... BUT after you beat the elite four, go into the house in route 114 the fossil maniac's house and go ito the cave he busted open. at the end of the cave there is the opposite fossil of wich you got in the desert. there is also lots of dittos in there!!!
Nothing really, he just gives you a "Dig" TM.
You get TM28 Dig from the Fossil Maniac's brother on Route 114.
That TM is given by a kid in the fossil maniac's house which is west from fallarbor town.
on route 114, go inside the fossil maniac's house. his little brother will give it to you.
trapinch is you don't let it evolve and when it's lv45 it learns it or you can get it by the little kid in the fossil maniac
TM28 Dig in Pokemon R/S is on Route 114 inside the Fossil Maniac's house.