Gene manipulation's always fun (How does that work with steampunk technology, you ask? SCIENCE!), but I think I'd go with mechanical enhancements designed to increase an animal's strength, speed, and durability, as well as uplift them into sentience (of course).

All this is well and good, but I haven't quite gotten down how to alter the personality of the uplifted Mechabeasts. For some reason, vicious animals given strength and intelligence after long operations performed without anesthetic don't seem to like their creator very much. So here I am, trapped in my laboratory, trying to create a Mechabeast that's powerful enough to take down the howling horde outside my door, but also won't join them once it realizes what I've done...twentieth time's the charm, right?