Easily Catch Familiars
When you encounter a familiar that you'd like to capture or fight, sometimes it will run away before you have a chance to engage it. There's a trick that you can use in your favor, though. Quickly open your spells menu and close it again. That will cause the familiar to change its course and possibly run directly toward you. Now you have time to catch up to the familiar before it can escape.
My Neighbor Tomtoro?
Clear the Hamelin area in the game, then return to the Temple of Trials. A group of NPCs will have gathered. Talk to the white furry one, who is named "My Neighbor Tomtoro," a reference to the Studio Ghibli film, "My Neighbor Totoro."
Text Speed Sneak Attack Exploit
Here is an exploit using the game's text display speed. By setting the text speed to slow, you can have Oliver cast an innocuous spell like "Seek Fortune" (on the overworld) or any of the interior spells ("Levitate", "Chart Chests", etc.) and while the text message is being typed in the message box, enemies will be frozen in place. This allows Oliver to catch (or avoid) enemies easily, since you can move Oliver while the text is being printed.
Note that the "Veil" spell (from Horace's Riddles sidequest) will allow you to sneak up on enemies with 100% success ... but only if you've purchased the "Jack in the Box" merit award .
The Lord Of The Rings Reference
Visit the Temple of Trials after completing Hamelin's main quest and talk to The Pig Iron Duke (the one dressed up like a Hamelin guard). He will say "You shall not pass!"