Exactly how I got the achievement. Long Gui + Deprotect + 999% + Meteor Javelin should get you the achievement.
Long Gui is surprisingly so much easier in this game I'm kinda disappointed :C
I still need like 3 trophies myself. One for capturing Don Tonberry (10 kills so far and nothing ;~
, platinum and...something else IDK. I need to find out which one.
+1'ing, although I didn't get it because of meteor javelin, I got it with pichuu's feral link. Long Gui is your best bet because it's really easy to get him up to 999% and he's very susceptible to deprotect.
And yeah, long gui is really easy this game. In XIII-2, at max crystarium and good weapons, although no one was ever in danger of dying it still took at least minimum effort. I don't know if they thought his fight took too long, or the fact that you can easily manipulate your stats and monsters in your favor, but none of the super bosses here remain a challenge at full levels.
The only issue I repeatedly have is with Yomi, and he's the only guy you can farm traps from so if you want to get all the weapons and some of the accessories... lol?
If you aren't at a comfortable level with Yomi, then I also recommend sab/sab/sen. The more sabs you have the better the chance of landing poison. And even though Yomi does a ton of AOE attacks, a sen with fringeward and a wound potion or two will be useful.
The first time I killed him I needed to use poison, but I had issues with landing poison as well. Don't give up, just keep trying throwing it on him.
Now I'm at the stage where I just deprotect/imperil/stagger/attack. There are probably easier ways to kill him but this is the way I'm comfortable with.
One more achievement left, for some reason I just
can't get the preemptive strike achievement. I don't know if one of my fragment skills are messing it up. Does anybody know if it counts while field killer is on?