Solving Horace's Riddles will unlock some handy spells for exploration and treasure chest looting. Once you answer all of Horace's riddles, you should have all the "optional" spells in the game.
Completing the rest of the story will earn Oliver the rest of his spells (and unlock the Trophy). Following up this long side-quest by completing Errand 136 will also award you with a very powerful Sky Tree Wand and alchemy recipes for weapons for Esther and Swaine.
PS3 Riddle Guide
Ding Dong Dell
You will meet Horace at the memorial shrine near the Ding Dong Dell castle entrance and get the Spirit Medium spell. Cast the spell to talk to him, which incidentally, completes this task.
Horace is near the milk fountain and will give you a new Tale of Wonder and ask you a few questions about it.
The third smallest target is the "DRAGON OF THE WEST"; you get the Draw Poison spell. Note you can spell the answer in all lower-case if you like.
Horace will be standing on a bridge overlooking the boats in the water. The answer to Horace's riddle is "FINEST FIBER".
Oliver will get the Vacate spell from the ghost. This spell forces Oliver and the party out of a dungeon (labeled "dangerous place" by the game) onto the overworld for the Travel spell to take effect.
Horace is in the outskirts of Fairygrounds, on the way to the Fairy Godmother. His riddle answer this time seems to be "CRISPY LETTUCE".
He gives Oliver the alchemy formula for Sage's Secret.
Horace is on the balcony overlooking the main street below (this observation platform is outside the Hootique). Horace's answer should be "5" (for the number of Automata familiars in the Wizard's War mural in the Familiar section of the book).
Oliver will get a Chart Chests spell, which functions like a radar for chests.
Horace is in the Yule Elder's house, looking at a Blizzard Bloom. Answer the riddle with "BLIZZARD BLOOM" and earn the Cloudburst spell.
Return to Ding Dong Dell
Horace will be back in Ding Dong Dell after the events in Nevermore, and after the event that follows it, if you've answered all his riddles up until now. Find him at the cemetery in upper Ding Dong Dell. The answer this time is "UNLEASH" and Oliver will learn the Thunderstorm spell.
Horace will be awaiting you in the Ara Memoriae if you answered all his riddles till now and defeat Gallus half-way through the Ivory Tower (to unlock the Astra wand, otherwise, Oliver can't cast the reward).
Horace will be at the northern most "pot", and asks you to give him an answer of "WIZARD'S ROBES".
(If you're wondering where this is found in the Companion -- it's the entry for Wizard's Robes on page 117. Some of the letters in the description are written in a different color to spell out the word "beware". Proper subtle, en't it?)
Upon answering this, Oliver will get the Astra spell. Strangely enough, Oliver can cast this spell in battle without the wand of the same name that was earned from Gallus, but defeating Gallus is required for Horace to appear at Ara Memoriae.
This riddle also unlocks Errand 136, which involves a few more riddles as you follow Horace around the world.
NDS Riddle Guide
Ding Dong Dell
In the Japanese game, when talking to him for the first time in the Kingdom he will ask you to accept a quest. Upon accepting, he asks three questions, if answered correctly you receive three strong coffees (ばっちりコーヒー 'right on the mark' coffee):
- 1.「マジックマスターの最後のページに描かれている太陽はどこに描かれている？」Question 1: "In the Magic Master's last page, a sun is supposed to be drawn. Where is it drawn?"
- 『右上 Upper-right』（答え / Correct answer）
- 2.「マジックマスターの最後のページに描かれている人は何人？」Question 2: "In the Magic Master's last page, how many people are in the drawing?"
- 『4人 4 people』（答え / correct answer）
- 3.「最後のページに描かれている流れ星が流れているのはどっち回り？」Question 3: "In the Magic Master's last page there is a falling star, which direction is it flowing?"
- 『反時計回り Counter-clockwise』（答え / correct answer）
- 1. Miranto: "よし まずは マジックマスターの１３ぺージを開いてくれ。この１３ページに描かれている魔法使いが なんてしゃべっているのか分かるかい？" Ok! First, it's drawn in Magic Master's 13th page. In this 13th page is drawn a wizard but, do you understand what it's saying?". You'll win 3 stamps (I think).
- 「なるほど I see/indeed」（答え / correct answer）
- 2. Immediately after, he will ask you another question: "１３ページにはアストラム語がもう一つ隠れている。そっちも解読して答えてくれよ。"There is one more hidden thing on the 13th page in the Astram language. Like before, give the deciphered reply." If you answer correctly, you receive (ミストローブ Mist Robe) and 3 stamps.
- 「さいこうきゅう highest grade/top class」（答え / correct answer）
In Al Mamoon (ババナシア王国 Babanasia Kingdom), you'll accept a quest from him. To complete it, go inside the weapon shop and click on a blue sparkling thing inside, then talk to him again.
In Castaway Cove (港町ビッキーニ Bikini Harbour), you'll accept a quest from him. Talk to a villager in the very leftmost part of the village, she'll give you a recipe for "raw caramel". Make one and then give it to Horace/Miranto.
In The Fairyground (デル・モカール Del Mokaaru), he'll give the quest "あるルーンの成り立ち". The answer is "3".