Final Fantasy XIII

This achievement is for defeating the mark for Mission 54, a Gigantuar.

After trying numerous parties, setups involving Sentinels and what not, i've found that luck is your better bet for completing this mission/achievement. As well as 5 starring the mission (if you're going for 100% completion on this game).

My party was as follows, and you should be more than fine if your party is somewhat similar.

Lightning (leader) - 15135 HP, 1550 Strength
Fang - 19455 HP, 2101 Strength
Vanille - 15955 HP

I used only one paradigm, Tireless Charge (COM,COM,MED).

NOW HERE'S THE IMPORTANT PART.
Equip your Lightning with either Lionheart or Ultima Weapon (preferred), for her quick stagger ability. Now for her accessories, equip her with AT LEAST a Speed Sash. The combination of her Weapon and the Speed Sash accessory will give you a RANDOM ability called Instant Chain.

Instant Chain will occasionally fill the enemy's chain gauge all the way up, making staggering really easy to achieve.

This may take you a few battles, and you may die a few times since you are relying on the luck of instant chain, but it is almost guaranteed you will 5 star this mission using this method.

First of all, use an Aegisol and a Fortisol before you approach the mark. Basically just have Light and Fang constantly Attacking while Vanille cures. (it may help to have her Healer's Staff for improved cure) Keep going until the chain gauge instantly fills up, stagger the enemy and keep pounding away with Fang and Lightning while Vanille cures. Before you know it the Gigantuar will fall.

Once again it may take a few times of dying or losing the battle. Just keep retrying with the same strategy and Instant Chain will eventually work it's magic.

Complete Mission 54 on Gran Pulse.

A link to a guide that show's all the locations for missions and their marks.
http://www.gamesradar.com/f/final-fantasy-xiii-cieth-stone-m...

The following video shows the encounter:

After being stuck on Gigantuar I used certain accessories that helped me Defeat Him in under 2 minute These Certain accessories have Things attached to them called "Instant Chains"
the Following accessories Have instant chains attched to them Speed Sash + Survivalist Catalog

Energy Sash + Warriors Wristband

Speed Sash + Champions Badge
Speed Sash + Hunters Friend
I used Fang,Lightning and Snow.
The instant chains DON'T always work but,With everyone in the Party there's a 15% chance of a instant chain happening.
The paradigm's I used to Start this battle was SAB/MED/SEN.
And as the Battle first starts hurry and cast Daze on gigantuar and when it sticks Switch To COM/COM/COM then The Instant chanin should kick in and from the point on the battle is yours.
If doesn't work Retry Good luck if have any questions feel free to ask : )

One way to kill the giant cactus is to insa-stagger it.
What I did was get Light,Fang, and Vinille. Make Fang the leader and give her the power sash, speed sash, ect. to get the ramdom Icon that comes under the stats that says Random: Instant Stagger. Now also do that for Light. Now both have insta-stagger. (shrouds would help to) Now have the classes set up.
-Fang/Light/Vinille
-Com/Rav/Med
-Com/Rav/Rav
-Com/Med/Med
-Sen/Med/Med
-Com/Com/Rav

Now its just trial and error from there. Cross your fingers and hope to get lucky on the insta-stagger. Good luck.

This achievement is unlocked by completing Mission 54—the Bigger They Are. You have to defeat a Gigantuar who is very fast and has a devastating 10,000 needles attack. The best approach is to rely on luck using a Random Instant Chain (RIC) strategy. RIC staggers instantly. Gingantuar has low HP and the single stagger will do him in. This can be done either in chapter 11 or in post-game play.

Luck comes into play because RIC has less than a 1% activation for a single hit. However, by making two party members RIC capable and using Sazh’s multi-hit Cold blood, you can change a low percentage into a probability.

Equip Sazh with one of his four RIC weapons--Rigels, Polaris Spl, Betelgeuse Custom, and Procyon. Equip him with one of those and one or two accessories from the following group (but not 3 which will negate the RIC)--Surv. Catalog, Champion's Badge, Speed Sash, Energy Sash, and Hunter's Friend. Give Snow the Midnight Sun or Unsetting Sun for RIC and one or two accessories from the above group but not three. Fang's not going to RIC so you have more freedom with her weapons and accessories

Sazh Snow Fang

Sen Sen Sen
Rav Sab Sab
Syn Sen Sab
Rav Sab Com
Com Com Com
Med Med Med

Suggested Equipment:

Sazh: Speed Sash (for RIC), Pain Dampener, White Cape
Snow: Survivalist Catalog (for RIC), Diamond BangleX2
Fang: Aurora Scarf and Nimble Toe Boots (for ATB charge) Power Glove

We have some latitude in the accessories once we equip Sazh and Snow with at least one RIC-triggering accessory. I suggest Pain Dampener and White Cape for Sazh to protect our leader against pain and fog respectively which are often side effect of 10K Needles.

At the outset, use Librascope or cast Libra. This will inform the AIs of Snow and Fang that Gigantuar is vulnerable to Daze. Immediately switch to Rav Sab Sab (you’ll have a full ATB bar) and execute Cold Blood. Chances are that one of Sazh’s 17 hits will stagger it. If so, switch to Com Com Com to finish it off. Odds are also in your favor that Gigantuar will be dazed. If Gigantuar is not staggered, go to Syn Sen Sab and cast enfire on everyone’s weapon. The ATB bar will be charging while you set up your commands. Fang will continue to inflict daze. Snow will act as a sentinel and allow the party to survive a 10K Needle attack if you’re not able to switch to SEN SEN SEN fast enough. Chances are Gigantuar will be dazed and will not attack.

Go to Rav Sab Com. Your ATB bar will be full. Execute another Cold Blood. Snow will hit Gigantuar with Daze while Fang will do major damage with her enfired weapon. The odds are really in your favor now that Gigantuar will fall victim to the RIC and be staggered. If so, go to Com Com Com and finish him off.

If our Green Giant has the luck of the Irish and survived another attack, the best course is to go to Sen Sen Sen, use a potion or two even if you don’t need it. This ensures that Gigantuar will target someone other than Sazh as the other two members provoke it while the item is being used. Right after the 10K Needles attack, go to Rav Sab Sab and hit him again with Cold Blood.

Continue the pattern of sheltering in Sen Sen Sen and attacking with Cold Blood in Rav Sab Sab until you’re successful. You have Med Med Med in case you need emergency healing above what the use of items can give you in Sen Sen Sen.

Whether or not you are successful, this will be a quick battle. If you fail, reload your save and try again. Even though this is luck based, the odds do, in fact, favor you.