Ok I will post the things the strategy guide wrote, and my own personal thoughts with it. So here it is.
Desthscythe is not that effective if you know your way around Marluxia's attack range. Just avoid the GIANT SCYTHE BLADE and you'll be fine. Blossom Shower however is the only attack that is very affective unless you have a 0 card.... but if not you can't avoid it so back away from Marluxia when he casts this, because after it hits you he will slice at you after it.Marluxia is an enigmatic foe. You'd expect him to be extremely difficult (His attacks are really impressive looking), but he doesn't seem to inflict the kind of damage that you'd expect. Marluxia's weapon of choice is the scythe. This weapon gives him longer than average reach and extends his normal attack range from simple strokes to dramatic slashes. In addition, Marluxia has access to two big sleights: Deathscythe and Blosom Shower, both of which are double boosted by his Double Sleight ability.