I recommend to add different new types of parts here's my suggestion:
Missile Arms: similar to how Cyborg ability works ,give The mech mastery a rocket launcher on both of he's arms ,he can still punch and all but the only thing it can do is launch it ,it will instantly explode If it hits a solid object or a user.
To make it slightly unique if they tap The E or Q again after launching the rocket launcher it would instantly explode creating a small shockwave similar to pulse Q
Shockwave: Deals 15 dmg (in exchange of creating a shockwave it doesn't do the original explosion anymore that deals 23 dmg)
Missile when hit: deals 23 dmg per hit.
Will be unlocked after 25 kills similarly how other mech parts are gotten.😄
The Image of the Mech Arms Are designed Into a blocky square missile type it's Edge are pointy too resemble a missile