I'm ignoring Artifact sites, this is too hard for me. I know what some people did them even on Superhuman, but not me until I get sonic weapons and MC protected guys. Usually I just land there and only fight first stage if it has Gilman (no MC and terror units on pyramid map) or shark mobs which has Navigator. The last one is dangerous if you get unlucky and Octs spawn with them too. Then I abort, Oct MC is nightmare. Sometimes I try Aquatoids (navigator present) and Tasoth guys, but only if I have turtle to block the Triton door, so panicked guys won't leave it easy. Need keep eye and unequip all explosives include disturbance grenades. Weapons on the floor too. Long and patience, but if thing goes bad, tank get destroyer or low health just abort -750 score + score from killed aliens is better than full wipe. Total month score could be nullified doing landed very small (beware they could up and attack you, but now it's easy to detect because of circles), small or medium USO's. And if you got drills you could melee any aliens who came close to Triton door. Even underwater scout drone without weapon could shoot if you equip gas cannon or whatever you like. Shoot, put weapon down to avoid big time units penalty and repeat. Beware disruptor pulse launcher on medium USOs.