Bosses: Note however that as your Bard progresses in the game, he can get an Enhancement to effectively fascinate constructs and undead (Music of Makers and Music of the Dead). They are optional, but it will be a big help when you do take the Mabinogi Gold enhancements as a lot of dungeons are infested with the mentioned creatures.
While it is a viable option to use Fascinate, a Bard has to accept the reality of only having a few songs he can use between rests. That is, your Bard's Fascinate can be limited.
You can take enhancements to increase the number of songs. For example, you can take Extra Song VI and you can perform 10 additional songs before resting. But in case you don't have these enhancements, you can always rely on Otto's.
Otto's Resist-able Dance - Level 1 spell that causes creatures to start dancing, was rendering them helpless. Otto's Sphere of Dancing - Level 4 spell that compels enemies to dance when they enter a magical sphere.
Downside is that Fascinate doesn't work on:
Vermin (spiders, scorpions)
Oozes (all types - purple, gray, etc.)
Undead (skeletons, wraiths, ghouls, ghasts, wights, specters)
Constructs (war-forged, golems, and the tough mechanical dogs)