Mission 31: Eliminate the Bully Dog

Mission 31 in Kingdom Hearts 358/2 Days sends Roxas and Xion to Beast's Castle, where they decide to try an experiment to restore Xion's Keyblade.

Regular mission
Eliminate the Bully Dog.

Story summary
Saïx refuses to send Roxas and Xion on anymore missions together. In one last, desperate attempt to keep him from finding out about Xion's loss of power, Roxas lends her his Keyblade, hoping its familiar feel might bring back her ability to again summon her own. It works; upon the defeat of the Bully Dog, Xion is able to summon her Keyblade once again. They celebrate with Axel and some sea-salt ice cream, expressing their wish that their friendships all continue forever.

Mission walkthrough
Before you start, equip yourself with as much magic as you can! You'll have a stick for the entire mission and you'll need to defend yourself because your Strength will be reduced. Ethers (and Hi-Ethers, if you have them) will also come in handy, though you will find quite a few on the mission as most of the treasure chests contain them.

You'll enter on the high platform of the secret passage. There are enemies all around, a couple of Mega-Shadows and Snapper Dogs apiece. You can head straight for the exit to the West Hall, but you'll miss out on some chests down below if you do.

Continue into the West Hall and beat more of the same Heartless until you reach the south end. There, you will see Cogsworth. You're going to have to sneak past him as usual. Just stay out of his red range of view and you should be fine. This time, he makes a roughly circular pattern in the center of the hall. He will occasionally make a quick glance, but for the most part stays looking in the direction he moves in. In spite of the narrower hall, it should be pretty easy if you watch him carefully.

Once you're in the Entrance Hall, you'll probably want to slip down into the main part. There's a Bulky Vendor waiting at the base of the stairs, as well as a couple of treasure chests. Make sure Xion is right behind you and not hung up on the stairs, or else have some magic ready, as your stick isn't going to cut it if you want to beat the Bulky Vendor before it disappears. There are also a couple of Sergeants in the center, roughly between the two chests. Once you clear everything out, make sure you've restored your magic with Ethers before you head into the Ballroom.

After a short scene, you'll find your target, the Bully Dog. Before you engage the Bully Dog fully, you'll want to run and grab the chests in the Ballroom. Fire magic in particular seems to hurt the Bully Dog. After the fight, you automatically RTC, so you won't have to worry about making the return trip sans Keyblade.

Challenge Mission
Being capped at Lv.5 makes this mission tougher, and to get all three sigils, you have to complete this mission in less than 45 seconds. Remember, you're equipped with a stick for this mission, so forget physical attacks and go straight for magic. Have max Haste equipped so that you can run around to dodge the Dog's attacks, then cast Lv.5 Fire or Fira, and have plenty of them. Glide if you have to, but remember that speed is of the essence. Take out the dog quickly so that you don't lose a sigil while running back to the RTC point.

This will be one of the harder missions, as you are not only capped at Level 5, but the boss is far stronger, meaning that one hit will likely knock you out. The key here is to keep moving, using High Jump and Glide to fly around and avoid the Dog's attacks. Wait for an opening, then use Fire Magic to damage it. As you are equipped with a stick, you can't rely on a special Keyblade's power, so make sure that your Fire magic is at Lv.5 and that you have lots of it. Bring Elixirs to replenish your magic if necessary.