Floor 6

Right as you enter Floor 6, you'll be locked in a room with a Geozard. It looks similar to the Zora Warrior from Phantom Hourglass, but don't worry, it's easier to handle with Phantom Zelda's help. Have Zelda distract the Geozard by tracing a path into it so a crosshair appears. She'll engage it in a sword fight. While it's distracted, sneak behind the Geozard and slash its back. Keep repeating this until it's defeated.

After the Geozard is down, the door will open. Follow the hall into a room containing a Mounted Miniblin. These are tricky, and you can only deal with them while riding Zelda. To the right, there's a high ledge, but it's blocked by a constant flamethrower. Trace a path for Zelda to cross the flames, and then use her as a shield to walk through the fire without getting hurt.

Once you're past the flamethrower, get on Zelda and defeat the Mounted Miniblin with a slash. Continue heading east, being careful of the flamethrower on your level. If you need to stop Zelda's movement, just tap the icon at her feet. While still riding Zelda, use the Whirlwind ability to knock a small key off its perch. Guide Zelda over to the key, and you'll automatically pick it up.

Head back west, then north into the center room. Defeat the Mounted Miniblins in this area, then hop off Zelda. Use the small key you found to unlock the door, and then head upstairs to continue your journey.