My first and so far only quadrupedal mech, Eviscerator was based off a name rather than a general idea. I'd like to say I nailed it. I went all in on the anthropomorphic, mechanical, not-quite-reptile look. As far as fictitious weaponry goes, Eviscerator has no other weapon than the focused nuclear charge it blasts out of its mouth once latched on to its target.
Eviscerator was the only mech in its universe that didn't house a pilot. I wasn't too displeased with this since it was different in a couple other ways too. As a quadruped I gave it a movable spinal structure, and I think it turned out fairly well. Originally the idea for the focused nuclear charge was that it would project out of the stomach section of the mech, and it would simply latch itself onto a target to fire. I thought the whole mouth thing was a pretty awesome improvement, even though there are no actual additional pieces below the head to suggest such a weapon system.
Eviscerator turned out to be my most Bionicle-heavy mech, but I think it still fused rather well. I hadn't really seen Bionicle elements fused into System mecha before, so that was pretty much an original thing, and it helped emphasize a specific aesthetic and allowed for the use of some more specialized pieces such as hands, heads, and feet, that I would otherwise have had to build myself and likely make larger and bulkier than they needed to be.