Sectopod (Bureau)

A large quadraped mech, with a Sectoid pilot: a heavy unit with thick armor plating, heavy weapons fire is required to destroy it in a head-on fight. Or, use targeted shots to destroy the canopy, then the pilot, or somehow get a view of the back of the fuselage (flank it or distract it), and target the plasma pipes on the rear.

It is essentially a mobile Gun Turret, with a melee attack.