"Hoisted by his own petard!"
You roll this thing up to a gate, and detonate the charge placed in the bell shaped "muzzle" and blow the gate and the petard up.
Added an attack animation for "usefulness", even though a petard is pretty much a "one-shot" melee cannon. But who knows, maybe someone wants a weird bell shaped cannon.
Hand-made animations for once, but the particle emitters is shamefully stolen from the WarWagon (wc3 vanilla version).
Edit: Added some sound effects to death and attack
Keywords: siege, weapon, warfare, castle, gate, demolish, sapper, suicidal, explosive, explosion, attack, petard, rolling, medieval, cannon, bombard