Defiance Free to Play

The Emine arena is by far the easiest of the bunch. The enemies you face are low-level raiders (rioters, blitzers, and the occasional tanker) with some afflicted thrown in later on (mostly flailers and sickos, with a trembler or two). It also features environmental hazards in the form of flamethrowers, but you can easily jump over these without setting yourself on fire.

As the rounds go on, there are several factors in play that significantly reduce the number of enemies available to kill, which makes it nearly impossible to maintain your multiplier beyond round 2. Fewer cannon fodder enemies spawn in lieu of the larger ones, the raiders and afflicted fight and kill each other, and a greater number of the flamethrower traps activate more frequently which cook the rest. Fortunately, there are enough enemies to simply dash between them and kill them at your leisure while still collecting enough points to gain the gold medal.

In an ideal run, collect around 3500 points in the first round and hover around 6500 by end of the second round. I was able to hit the gold medal 10000 by the end of the third round, so I was using the fourth and fifth rounds almost exclusively to hunt golden skitterlings. Don't forget that you get 2000 points for not dying (X button self-revive is okay, A button extract is not), so acquiring the easy 3500 points in round 1 means you only need 1125 points for each of the following four rounds, which is completely doable with almost any setup.

Because you're going up against groups of afflicted and rioters, you're going to need a weapon to bypass the riot shield and level groups of enemies quickly. This means detonators. If you max out and equip the perk called Deadly Cascade (first row, seventh column, above the overcharge tile) your explosives do 30% bonus damage per enemy caught in the explosion radius, which often means only one or two detonator rounds will vaporize entire mobs. Because enemies continuously thin out as you go on, you want to check your minimap often for groups of enemies and chunk detonator rounds in there for tons of easy points. It's infrequent, but it does happen.

For all arenas in general, you need something you can fire from the hip. Taking the immense speed penalty and tunnel-visioning on a single enemy to ADS (aim down sight) is what's going to get you overwhelmed extremely quickly. If you have not discovered the wonders of the VOT Pulser, the arenas are certainly a good place to become familiar with them. They are equally as accurate from the hip as they are when ADS (as is evident when the reticule actually expands when you do so), and equipping a maxed Gunslinger perk (ninth row, fifth column, right of the cloak tile) gives you a whopping 12% critical multiplier from the hip. If you get a good Pulser with several critical rolls you can wreck everything from the hip with little effort, inside the arena and out.

I recommend Respark shields in general, since their recharge time is the lowest of any type (three seconds of not receiving fire to begin recharge) and they regenerate moderately quickly (40% of total shield capacity per second) for a slight penalty in total capacity (about 80% of what an Ironclad or Hurricane would have). Some shields offer a large capacity but do not regenerate for 6 or 9 seconds which is an eternity when you're in the midst of a firefight, especially when you're in an arena that requires you to go find the enemies for score. Regardless of the shield type you choose, a Regenerator variety gives you 25%-75% health regeneration depending on its rarity, which is invaluable because health does not regenerate on its own.

To make a quick recap, these are my recommendations (and the setup I used in this arena):

Weapon 1: VOT Pulser (the higher the critical, the better)
Weapon 2: FRC Big Boomer/Matchlock Boomer (ground pounders are okay, but the initial explosion does no damage and the bomblets are unpredictable)

Shield: Respark Regenerator
Grenade: I'd go with Frag, Cluster, or Pyro. If your low multiplier in later rounds is bothersome, perhaps Hatchling
Spike: No matter, you shouldn't be standing still long enough to use it
Stim: Heal

Ability: Decoy

Perks (row/column):
Assassin's cache, R10 C4 (regenerate ammo on a critical kill)
Kill or be killed, R9 C7 (huge critical multiplier when your shield is empty)
Execution, R7 C4 (recharge shield on critical kills)
Fortitude, R4 C5 (extra health)
Deadly cascade, R1 C7 (bonus damage for each enemy caught in explosion radius)
Gunslinger, R9 C5 (extra critical damage from the hip)
Detachment, R3 C4 (each kill reduces damage taken)
Thick skinned, R3 C7 (half damage for a moment after your shield breaks, great for getaways)
Failsafe, R4 C3 (take less damage while shield is recharging)

For this achievement you need to get 9999 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!