Archers and mages are your only weakness. Do not chase them. Let your pet tank the arrows while you Stomp the melee units. Then, use line-of-sight (hide behind a pillar) to force the archers to walk into your hammer range.
But Torchlight 1 has a deceptive amount of depth. A poorly built Destroyer will chug health potions like water and die screaming in the deeper levels of the Shadow Vault. A correctly built Destroyer doesn't just survive—he turns entire screens of enemies into loot pinatas. torchlight 1 destroyer build