Oh my god, how can one even possibly defend against that without making sure all your troops are immune to MC?
Well, high ranking Tasoths = M.C. attacks. Keep a lightning rod or three on the team (soldier with Low M.C. strength who has been targeted on previous missions by M.C. attacks), and unarmed so they can't hurt themselves or others. Let them soak up the M.C. activity.
We have good armor here, so use scout and snipe tactics. The Tasoths will respond well to sonic weapons, or sonic disruptors (alien grenades). Apply liberally. Tricenes should also be vulnerable to explosives so that may help there too. Other than that, if you don't have a squad that can handle this level of a terror mission, just touch and go. Land, wait one turn (let the enemy burn his TUs), pop the door open, shoot anything in sight (ok, leave the civs alone, just shoot the extra-terrestrials (extra-aquestrials??)) and then abort. You will lose points, but far less than you would have if you ignored the terror mission.
