invisible goblin is easy, just make sure that you use fire succubus, centaur, mermaid, dwarf engineer, and goblins. send your hero to the middle to kill goblins and just build up your army and then use fireball to take care of the bombermans. you attack when the unit cap is reached, when you come close to the invisible goblin, use the lightning spell to stun it and also the ice spell to freeze it if necessary. continue attacking and you'll win; don't retreat when the enemy counterattacks
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