I've seen many YouTubers comment on the kickback that cannons have, and the trouble they have making a sturdy enough build to survive multiple cannons. B2B50 has taken that kickback and turned it into the propulsion system of a very simple, but very effective, two-stage rocket.
I've also seen a lot of humanoid siege weapons around (including a Besiege version of QWOP that's just as hard to operate as the original). But there's just something fun about this design. I don't know if it's the faceplant or the exploding sheep that makes me smile more.
A medieval Optimus Prime! There's something charming about a wooden and steel Transformer, and I think the flamethrowers definitely add something the original missed. Maybe this style will be the next steampunk? Medipunk?
This bone dragon, complete with flaming eyes, is just stunning. Indigo, the creator of this masterpiece, says it took him four days to create and can only be run on invincible mode (as it's quite unstable). Indigo has very awesomely posted this dragon for download. If you also want a fire-breathing dragon (that could explode horribly at any second), check out this source link.
A fire-powered ninja! This is a great use of propulsion to make inherently unstable two-legged machines work. Sure, you could just fling the metal guy into wind mill, but the sword adds that extra class.