Mission 56: Eliminate both giant Heartless
A Heat Saber and Destroyer have surfaced in Twilight Town. Team up with Axel and Xion, find these Heartless, and eliminate them at once.
Since Xion just woke up from her prolonged coma, Saïx sends Roxas, Axel, and Xion to Twilight Town. This makes it the only three man mission in Kingdom Hearts 358/2 Days.
First you must defeat the Heat Saber who is at the Sandlot. This fight is tricky because a Barrier Master is here to assist the giant Heartless. Take out the Barrier Master by knocking it senseless and blasting it with magic attacks. Once it's out of the way, you can focus on fighting the Heat Saber.
The Heat Saber acts the same way as a Dual Blade, and its attacks may ignite you on contact. Attack it with combos until it blocks. Dodge or block its striking attacks. If it starts charging its energy, prepare to block as soon as it starts to strike. If you block the attack, the Heat Saber will fall backwards, leaving it vulnerable to your attacks. Blizzard magic is especially effective. Try to hit the Heat Saber with Blizzard while it's charging to leave it vulnerable for longer, especially to more magic attacks.
Once it's defeated, head up to the Station Plaza. Xion collapses in a cutscene, and Axel takes her off to the side. This leaves you to fight the Destroyer alone. Ignore the Minute Bombs during this battle, and focus on the Destroyer. Avoid its laser attacks by dodge rolling to the side or underneath it. Countering the attacks with Thunder magic will disrupt the lasers and cause a good amount of damage on the boss. Continue dodging and countering the Destroyer's attacks and striking with your combos and it will fall soon enough.
Bring plenty of Blizzard magic, especially Blizzaga, to speed up the Heat Saber battle. You'll want to knock it down as much as you can. If you have room, bring Thunder magic along for the Destroyer battle. If you find your health dropping into the yellow zone, save your limit breaks for fighting the Destroyer. They will be a significant help.