Equip enough Potions on your panels slot before starting the mission "Collect Hearts in Twilight Town". This mission requires you to kill all of the Dire Plants in the mansion area and defeat a strong heartless, Zip Slasher, in order to fill the mission gauge completely. After eliminating all of the Dire Plants in the mansion area, get out from the woods. A caution sign will appear to tell you that a strong Heartless is near. Defeat a weak Shadow in front of you, then go to the big alley (the entrance is between two houses) where the tram is stopped to find Zip Slasher. He has great health and defense, a strong attack, and is immune to Fire magic. Instead of attacking him first, get away from him and let Marluxia slash him until he does his only attacking move, Spin and Stab (first he spins with his knuckles blades then stabs with his weapon). This move does insane damage. After the Spin and Stab, he will start standing like a statue (not moving at all and probably recharging his attacks). Unleash a barrage of Keyblades slashing strikes until he guards his body with his knuckles blades. When he does this, immediately run away from him before you get hit by a Spin and Stab. After he does his strike, attack him again with your keyblades and run away quickly when he defends himself with his blades. Repeat until you win. Note: Whenever Marluxia's health falls to 50%, he will use Curaga, which heals you too.