The post-game Errands in Ni no Kuni are a bit more robust than the ones in the main game, and understandably so - they're supposed to be an extra challenge to keep the player going. Such is the case of Order of Illusion, where some servants of Queen Cassiopeia have come calling…
Enter the Ivory Tower (it's floating near Ding Dong Dell) and head north from the entrance. There are three knights standing near the first waystone in the place, and they need your help. Agree to the task Order of Illusion and you'll receive a task that's been a long time coming: destroying the robots found scattered throughout the lands of Ni no Kuni. You've seen their fallen forms before, and now you have a chance to blow them up. Do you remember where to find all four Magimechs?
Travel back to Golden Grove and enter from the north. Follow the path south to the second split and take the road east. Go east through the dirt furrow then north until you see some jumping mushrooms that lead west. At the top of this rise is the first Magimech.
Enter the volcano and go straight north. The Magimech waits for you in a small clearing where once you had to face a bounty fight with a Magmoiselle.
Run along the trail to roughly the halfway point, an old, abandoned cabin. Floating beside the cabin is the third Magimech.
Your final Magimech battle also takes the longest to reach. proceed into Glittering Grotto, using the secret paths you found during your first trip, to the lower levels. When you reach the tiered area full of branching paths, go east to the large, flat, snowy area. The Magimech is waiting atop a small rise.
The Magimechs do, indeed, hit a lot harder than the ones in the Ivory Tower. Fortunately, they have roughly the same amount of HP. So long as you have a decent amount of health going into each battle, you'll survive just fine.
Return to the Ivory Tower when the job is done. Turns out it's only just beginning, as there are three Magimech Masters that guard three ancient cities of Nazcaa: Nazcaa itself, Tak'al, and Itzos. The cities are gone, so you'll have to find the Magimechs on the world map by looking for pictures on the ground.
Finding the Magimechs sounds a lot tougher than it actually is. The only pictures carved into the ground are on the continent of Nazcaa, so that's where you'll find all three Magimech Masters. Land in the south and loop around the island to find them waiting. They're slightly stronger than their kin, and more likely to use magic, but the Masters are still pretty easy to destroy.
Return to the Ivory Tower, save at the waystone, and talk to the lead knight. You'll learn that they're also carrying Magimechs, and they want to scrap. Bet you saw it coming a mile away.
Fighting three of these stupid Magimechs is a heck of a lot harder than fighting just one. The primary danger is their all-hitting Twinkle Twinkle, as it tends to get used by two of them in a row. Until you get rid of one of them, it's best to leave your team in All-Out Defense and run around the room as Oliver, peppering them with Evenstar, Astra or another powerful all-hitting spell. Get rid of one and the battle becomes significantly easier to manage. Try to leave the Manic Magimech until last, as it has the most HP. Winning will earn you a Riddle Rivet.
After the battle's over, the knights will bestow a massive gift on the party: a Nazcaan Longsword, a Suit of Nazcaan Armor, a Nazcaan Helmet and 10000 guilders. This is some of the best equipment in the game, and the Armor and Helmet in particular will make surviving elemental spells a lot easier. Enjoy!