Just thought I would mention one thing and see if anyone has anything else to add.

In Ys II, when fighting the late game boss that magic doesn't work on (not the final boss) try casting Time magic. In the DS version, this would actually work and slow down the boss, but in this version it fails in an interesting way. Try it!

(One little thing: on Easy mode, you can change your equipment/spells in the middle of a boss fight, making it perfect for checking things like this.)