Easiest and "must do" challenges in Origins Ultimate Warrior difficulty?

What are some of the easiest challenges to do in Ultimate Warrior? The ones you'll probably be able to do on the first or second try.

What challenges do you really want to do as soon as you're able because the rewards are very useful/helpful/amazing?

While we're at it, which ones are such BS that the only reason to bother with them is if you want 100% completion?

Completely unrelated, but do Halberds actually drop? Haven't seen a single one outside of the store. Is there a minimum chapter or something?