13th level Humanoid that's able to evade a 18th level party? That's a decent CR gulf to span. Classes alone probably won't do it, since classing something to level 13 means it should be balanced against other 13th level creatures, though min/maxing with an emphasis on evasion might slant that.
As a magic item suggestion, give the NPC a unique Artifact of your own creation that gives them additional evasive powers; probably something that locks to their person so high level PCs can't just snatch it from them to make them powerless. If you want them to just be hard to nail down, have it grant etherealness or earth glide (if underground a lot). If you don't want the Artifact to be a loot item the PCs get afterward, you might try something from the Weapons of Legacy supplement, where the item in question is an item that has quests/requirements to use it to its full potential, and the NPC has done the quest(s) but the PCs haven't/can't.
For the Lycanthrope aspect, normally a Lycanthrope build has to use an "animal" as the base creature type. Can you have this NPC through some means be a non-animal lycan with additional abilities? Create a Lyncanthrope build for a Displacer Beast or similar hard-to-nail-down beast; then the NPCs evasive abilities are intrinsic.
If I understand correctly, your problem is that any feats on Bard level 1 can't go towards Dazzling Display, because you need Weapon Focus first, and to get that you need 1 BAB. However once you're level two, you could, but you already spent the 1st level feats on other things.
According to the official FAQ, retraining is a great option for you:
Retraining: Can I retrain a feat to replace it with a feat I didn't
qualify for at the level I originally gained that feat?
Yes. As long as the new feat is a valid feat for your current
character, you can retrain the old feat and replace it with the new
For example, if you are a 3rd-level rogue who took Improved Initiative
at 1st level, you can retrain that feat and replace it with Weapon
Focus. Even though Weapon Focus has a prerequisite of "base attack
bonus +1" (which means you couldn't take it as a 1st-level rogue), it
is a valid feat for your current level (3rd), and is therefore a valid
choice for retraining.
(Note: Likewise, the fighter class ability to retrain fighter bonus feats does not require you to meet all of the new feat's prerequisites at the level you originally gained the feat.)
Here's how that would look for a 2nd level human Bard:
10 × your level × the number of days required to retrain
= 10 gp/lvl/day x 2 lvl x 5 days/feat x 2 feats
Total cost: 10 days @ 8h/day and 200 gp / 2 feats
Note also that
Some retraining options require you to work with a trainer. If no suitable trainer is available, the GM might allow you to retrain yourself by spending twice the normal time. Even if you train yourself, you must still pay the cost for training (though you don't double the cost as you do the time). Any option that requires a trainer also requires some kind of training facility for that activity.
I'd use a barbarian - Used a similar build like the following one.
Bonus feat: Throw Anything (no penalties with improvised ranged weapons - using a fork or a chair as a thrown weapon is awesome!)
Feat 1: Raging Hurler (can throw a two-handed weapon and double range increment whilst raging)
Alternate Feat 1: Point Blank Shot (for Precise Shot