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Ok, I have just completed this Quest, and I have tried, and tried, and tried, but it FINALLY PAID OFF!!! Ok, so I understand that this is NOT an easy Quest, AND these are fast Rajang we're talking about, AND they do a TON of damage... Ok, so the odds are against you. Really, really, REALLY... you get the idea. This ain't gonna be easy by ANY means. So, you're going to require knowledge, ridiculously powerful weapons, and a good set of items. Alright, here's the list of what I used:

-Weapon: Glorious Victory (hard to get Bow, but I'm pretty sure best in game)

-Armor: Monodevil (MAXIMUM LEVEL ONLY)

-Decorations: Ammo Box Jewel (x3) and Protection Jewel (x3). This gives you 'Adrenaline +2' and 'Load Up'

-Items: Potion (x10) Mega Potion (x10) Max Potion (x2) Well-Done Steak (x10) Mega Juice (x1~5) Mega Demondrug (x3 and up) Ancient Potion (ONE MAX) Bomb Material (x10) Flashbug (x10) Lg Barrel-Bmb+ (x2) Flash Bomb (x5) Shock Trap (x1) Genprey Fang (x2) Trap Tool (x2) Book of Combos 1, 2, 3, and 4 | Powercharm, talon, Armorcharm, and talon (1 of each) And Power Juice (I didn't use them, so you may not have to)

-Kitchen Stop: Eat Fatty Tomato and Dragon Tail for Health 140 and Attack Up.

-Kitchen Stop: Eat Kirin Cheese and Goldeenfish Brew for Health and Stamina +50

[edit] STRATEGY

Before you enter the Arena, eat one Well-Done Steak, one Mega Demondrug, and afterward, prepare your Flash Bombs. Now, the next step is crucial: AS SOON AS POSSIBLE, THROW A FLASH BOMB! You MUST do this to start attacking. Afterward, keep firing FULL CHARGE attacks while dodging the Rajang from close range, and keep circling it turning left and avoiding the walls. Or use Pierce attacks when it uses beams and other attacks while it is far away. It is not a very good idea to stay far away. Now, keep attacking it. Unfortunately, you'll probably die at some point, so when you do, prepare Flash Bombs. When you come in, make sure you are decent distance from the Rajang (or very rarely Rajangs) and use a Flash Bomb. Now, if there is one Rajang, then lay down a Shock Trap TO THE FAR LEFT OF IT! Now, carefully reel it in to the Trap, and Bomb it in the face. If there's two Rajang, skip this and attack from the left side. NOT THEIR LEFT, YOURS. If you're on THEIR LEFT, YOU WILL DIE. You should keep this up, and use Max Potions each first hit you take each life. Keep attacking like this, and with some luck, you should eventually have TWO (That's "2") DEAD RAJANGS!