You can craft some other things with the boss drops you get from the bosses in Cataclysm with the Mechanical-Fusion Anvil. Where you combine boss weapons to make them even better and stronger than ever before, with new abilities. Like the Void Forge which has a diffrent ability than the Infernal Forge where instead of a shockwave it instead summons void runes in front of you. There is also the Gauntlet of Bulwark, when combine with Bulwark of Flame and Gauntlet of Guard give you the Gauntlet of Bulwark. This new gauntlet lets you push enemies very far back and also does a lot of damage when doing it. You can make a lot more like Void Assualt Shoulder Weapon. I prefer not upgrading it as you can't give the Wither effect and you lose Howitzers as well. You can upgrade many things but you also have quests to complete that give xp and other rewards like even Nether Stars. Some are really hard like beat some bosses that are insanely tough but some are really simple and easy.
Mowzie's Mobs adds a ton of new bosses include Umvutha the Sunbird, Frostmaw, and Ferrous Wroughtnaut. But the main focus is the drops when you kill them. The Ferrous Wroughtnaut drops The Axe of a Thousand Metals that is better than any diamond stuff but bad once you kill harder bosses, he also drops the Wrought Helm which is an unbreakable iron helmet. Umvuthi the Sunbird drops a blessing thing that let's you harness the power of the sun and burn people alive. Then we have the Frostmaw which is a boss that