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.

The easiest way to win this achievement is to field a fully enhanced squad and win the mission. This means that all of your soldiers need to have at least one gene mod equipped. You can mix and match your squad with any combination of Gene Mods and MECs.