I defeated all the Caves already. About that little invisible goblin that does 999999 damage, don't send out any phoenix before you are ready! Use Goblins, Dwarf Engineers and 4 ranged units, and when they are all built to max you send your whole army at them. There will be so many goblins pushing back the invisible one that he can't do an iota of damage.
 "Epic War 5"){kind=icon}
 "BridgeCraft"){kind=icon}
 "Epic War 3"){kind=icon}