Complete Campaign on Extreme.

Very difficult.

Things to keep in mind:

* Enemies have more health and there are more of them.

* You will not have a VS suit for most boss battles.

* Your T-ENG decreases much faster.

* Shoot everything in sight. Everything that dies, breaks, explodes drops T-ENG which is your key to survival.

* The hardest boss is the first boss so save your energy because the game will get easier toward the end.