1. Hardest freestyle trick.If that means a trick that somebody can do consistently, I would have to say one of Salvador/Huitzi's crazy regen tricks. I'll go with Electric Spiders just because he himself says it is very difficult, but there are several others like Maximum Spider and Turbo Pascales.
If a trick that somebody can do once in many tries counts, I'll say one of the crazy catches by Matt Ritter in his videos, like behind-the-back bounce to between-the-legs blind-whip.
Finally, for the hardest freestyle combos, Gus is the King.
2. Hardest freestyle trick that you can consistently complete.UD boomerang to UD lasso/UD MGR. However, when I used to freestyle and tried it I could never nailed it on stage. But I am better now
3. Hardest "easy" trick for you to learn.Trapeze (when I think at my first attempts I have to laugh)
4. Easiest "hard" trick for you to learn.Staircase to Heaven