I'll make a few things clear. I suck with a good number of these characters. I won't go in the same order of the video but I'll list off the characters and how well I fare with them.
Warrior of Light: No doubtedly one of my better characters, even if his air game is a bit lacking. To say the very least I can at least beat 000 Feral Chaos with Warrior of Light, going with conventional method as opposed to the simple Level 1 trick.
Garland: He stands on middle ground with me. I have managed to beat 000 Feral Chaos ONCE with Garland, and never have I been able to do it again. The great thing about Garland is that he's can easily break foes within a few hits due to his initially high power. I only use this guy for showing off or just for fun.
Firion: Like Garland, I'm on middle ground with Firion. I prefer characters that have good ground and air moves. In all fairness though he does play a lot better in Duodecim than in the original Dissidia, I will admit to that. Firion is yet another character I have managed to defeat 000 Feral Chaos with.
Onion Knight: In the last game I could not stand using OK for two reasons. The first one was getting everything in his story is easily the most annoying task out of almost everything else in the original Dissidia. The second reason was because of his serious lag time after most of bravery attacks. But in this game, I actually enjoy using him. He's yet another character I managed to defeat 000 Feral Chaos with.
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https://www.youtube.com/watch?v=x6GPwk_6eso
In order to protect the balance of the world of Final Fantasy III, The Onion Knight and The Cloud of Darkness must join forces to defeat Feral Chaos and restore order back to their world. HUWAAH!!!!!
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https://www.youtube.com/watch?v=4VTSIHk6oio