[AlexanderHowl]

I would actually go with DR 4 [20] and Injury Tolerance (/4; Piercing Metal, -60%) [40]. At that point though, they become really problematic for anyone group in mass, especially if they also have Corrosive Attack 1d (Aura, +80%; Blood Agent, -40%; Melee, C, -30%; Symptom, 2/3 HP, Terrible Pain, +180%) [29] (each successful attack against the alien causes a spray of acid that causes agony to those burned).