In Metal Gear Rising: Revengeance, GRAD is a Ukrainian Unmanned Gear that is Chapter R-02's Research Facility level boss. It is known for functioning as both a bunker and a mobile combat vehicle. Its design is quite similar to Metal Gear REX, and returns as a sub-boss in later parts of the game.
This Metal Gear Rising: Revengeance boss battle is not known to be easy, as the GRAD ignores most kinds of damage. The Fox Blade, Armor Breaker, and normal HF Blade and Machete are ineffective against it, and it does not have a red weak point box to use Zandatsu on. On the bright side, once this boss is beaten, other GRADs will be nowhere near as difficult.
First Phase
The GRAD will fire all its weapons at Raiden, and the best way to avoid damage is to Ninja Run. Zig-zag between the doorways and use walls for cover. If close to the GRAD for too long, as it will then use a physical attack that will knock Raiden back. Raiden's support team will tell him that he needs to push the enemy back. The game does not do a good job at explaining how to do this though.
To push back the GRAD, Raiden can either use sword slashes or parry the boss's armor panels when it attacks Raiden in close range. Parrying tends to be the quickest method or by using Raiden's sliding combo attack. Once pushed enough, the GRAD will switch modes and a second fight phase will begin.
The Second Phase
For the second phase of the fight, it is best to get close to the GRAD and wear it down with light attacks. Eventually, Raiden will get the Blade Mode prompt to cut off its armor plates. EM Grenades can be quite useful in this boss fight, as they can stun the GRAD and give Raiden more chances to hack at it. If the boss moves away, stay close while also evading its missile attacks. Stay in front of the boss when hacking at it, as this is optimal positioning for parry if it melee attacks.
Once the armor plates are cut off, the GRAD will be stunned and Raiden can attack more without any issue. After the second Blade Mode prompt, the GRAD will be defeated. While more GRADS will be encountered in the future, they will not put up as much of a fight.
Metal Gear Rising: Revengeance is out now on PC, PS3, and Xbox 360.