KH Re: Chain of Memories (1.5 + 2.5 ReMIX) - Zexion boss fight
300This video features the boss fight against Zexion from Kingdom Hearts Re: Chain of Memories (the PS2 remake of the original GBA game). The boss can be fought only in Riku's story mode, Reverse/Rebirth, which is unlocked by beating the game's main story with Sora.
In the original GBA release the boss encounter of the Destiny Islands level consisted of just Darkside and Zexion was dealt with in a cutscene. The PS2 updated release added a proper boss encounter with Zexion right after the fight with Darkside, and also revealed Zexion's signature weapon, the Lexicon (a mystery that went unresolved since the release of the original Chain of Memories).
Note that this video was recorded while playing Kingdom Hearts Re: Chain of Memories on its 1.5 ReMIX version from the 1.5 + 2.5 ReMIX compilation for the Playstation 4 and on Standard difficulty. I was also playing on my Playstation 4 Pro.
The boss fight against Zexion can be pretty challenging because the boss has a rather unortodox MO. Instead of just attacking you with magic, attack cards and sleights, Zexion's cards and sleights are about stealing Riku's cards. Not only the stolen cards can't be used temporarily, but if the boss gets enough of them he will create three clones of himself who will use said cards against you, on top of unlocking new dangerous sleights to use against you (Dark Punisher and Catastrophe).
Whenever Zexion creates his clones, the best course of action is to destroy the three floating tomes he also summoned: not only you'll recover the stolen cards, but also gain some experience. Notice however that doing so can insert some "dud" Zexion's cards in your decks, which, upon activation, will damage and stun you.
As for all the boss battles in Riku's story mode, triggering your dark form and force the boss into a card duel are the best way to achieve victory easily