Defiance Free to Play

This arena is not too difficult. You need to score 10,000 points to get a Gold trophy for the arena, and you'll be fighting the standard mutant varieties. There won't be any hellbugs thrown in here like in the first arena. You'll only face mutants throughout, but they become tougher and more numerous each round. The special feature of this arena is that if you run through the blue gas clouds that periodically come out of the medical containers, it temporarily give you the effect of having used the Blur Ego power, so take advantage of the speed and extra melee damage.

In arena mode you score points by, obviously, killing enemies. Each type of enemy is worth a varying amount of points, with tougher enemies generally worth more points. The key to scoring well is to get your score multiplier up to x10 and keep it there as long as you can. With each successive kill you make, your score multiplier will go up by one, from x1 up to a maximum of x10. Pretty standard arcade type scoring. Also keep in mind that you will receive a 2,000 point bonus if you complete the arena without dying. You can use you self-revive without penalty, but if you have to use the A button to get back up, you will lose the bonus.

The Rizi Liro arena will be pretty well swarming with mutants for the last two or three stages, so 10,000 points should not be too difficult for you to achieve. Just try to keep a steady pace of kills to keep your multiplier up, and avoid panicking or getting surrounded. I pretty much stayed up top and next to the outside wall and let everything come to me for most of the fight and ended up well over the 10,000 points required for Gold.

Use whatever weapons you want, but I suggest a high firepower, large clip weapon like a light machine gun, backed up by a shotgun for emergencies. Make use of your grenade every time it recharges and go with either Overcharge or Decoy for your Ego power, since you can get Blur for free and Cloak is useless here. I used Overcharge in order to take down the large grenade launcher/minigun mutant bosses quickly.

For this achievement you need to get 10.000 points or more. I suggest to try the arena few times for learning the enemies spawn locations. The keys is the chains, you can get a maximum of x10, so try to keep the multiplicator more hight you can and use this combination of weapon and skills:
-Invader
-Respark Shield
-Decoy
-Nerves of Steel
-Single Minded
-Gunslinger
-Sucker Punch
-Fortified Stance
-Thick Skinned
-Cellular Armor
-Fortitude
-Kill or Be Killed (or better if you prefer)
This combination is what i've used for get the gold and i tryed it few times before write this guide, try to use weapon and shield purple or orange if you have it and Good Luck!