The Andromedon is a "hybrid enemy unit combining the intelligence of organics with the strength of machinery," which is to say it's a little guy inside a massive suit of armor. It appears to pack a conventional plasma rifle and is also capable of ejecting globules of the suit's coolant, which is corrosive against organic tissue and splashes for area effect. On top of all that, it packs a ferocious punch up close, and is immune to fire, poison, and acid, so enhanced ammunition is useless against it.
There are also "reports," to play along with the game's fiction, that the suit may be able to operate without its host, which almost certainly means that it can but Firaxis doesn't want to spoil all the surprises. If there is any justice at all in this world, the operator will hop down from the cockpit, then take the suit by the finger and say, "Come on, Mister A! The angels are waiting for our intergalactic tyranny!" Oh yes, I'm ready for dream time.
XCOM 2 is scheduled to launch on February 5, 2016.