Did anyone finish the Impossible difficulty?

I hope there'll be more enemies than just bloking player from saving.
Is there anyway to save game in this mode?

Which is the best weapon?

I divide weapons into 6 groups:

(1) Pistol

(2)Sniper

(3)SMG and MG

(4)Grenade

(5)Heavy weapon

(6)Rifle

Which is the best weapon in each group? I cheat weapon but don't know which is the best.

Another problem is the Allies guy with [i] above his head. He does not attack me but other Allies fire at him. Must I kill him to pass the stage? Why Allies kill one another?

Beside, is there any difference between Silent Storm and Silent Storm Sentinel?

I don't have a medic so, when a squaddie is wounded, what I can do to him? (I cannot use first aid kit and don't know which item to use)

One question left. In the abilities panel, do all upgrades cost 1 point or I have to accumulate points to get special upgrades?

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