Do what I did.
Get a trainer for invincibility.
yes I did have to cheat at points to beat the game.
The best weapon(if your not cheating)to beat the mercenary is the R-65.If cheating use the happy gun.I used it and beat him before he even got to me.
The happy gun is the upgraded light repeating blaster.But its not light anymore.It shoots the same thing as the tanks at a rapid fire pace.
Even with cheating its near impossible for ANYONE to beat the last level.
To beat the tanks in Theed-Happy Gun'em to death.
I have spoken.
"I hate the Autobots, I hate Cyclonus, and I'm not to fond of you either."