XCOM: Enemy Unknown

This is way easier with Enemy Unknown DLC activated as MECs with the right mobility upgrades can really dash through the train a great deal, I could finish this with 2 MECs and 2 snipers with Squad Vision within 4 turns, leaving 6 turns left.

Remember that you only need to activate the keypoints and not eliminate all enemies, so you can ignore them and just rush it, A Good MEC has tons of life and with the right upgrade that gives them -2 to all incoming damage, those overwatch shots dont hurt that much.

This can't be completed in base XCOM:EU with just SHIVs. It must be done in an Enemy Within game.