I think Horn Leech is the better move for Trevanent, but since you're running Rest, I think you can get away with using Wood Hammer.
Will O Wisp is one of the better moves for Trevanent. Definitely use it.

So I caught a Cobalion and Virizion already. Cobalion has an Adamant nature (Which can be useful for my X) and Virizion has a Naive nature which is also great.

Cool beans.

Say, have you used Forest's Curse at all? Or are or is adding a Grass Type to Pokemon not a good move for haunted trees to learn?

Well, unlike Trick or Treat, Trevanent can't make as much use of adding a type like Gourgeist.
If your moveset is looking to be Rest, Wood Hammer/Horn Leech, and Will O Wisp, I'd add a 2nd damaging move, like Shadow Claw or Phantom Force (Ghost got a pretty solid buff this gen, being able to hit Steels for neutral now), or perhaps a poison attack (For Fairies) or a random coverage move.

Why Hardy? It seems a waste to not pick a nature to actually boost the effectiveness of your Trevenant, either Adamant for offense or Impish/Careful for defense. Trevenant has no need for remaining neutral-natured and no business using Special Attack for anything.

Because it's the only Shiny I have that doesn't suck and I'll be training a normal Trevanant anyway with a better Nature for my Magiranger Team.

Ahh, taking advantage of a shiny. Makes sense. Other than perhaps putting those SpD EVs into Defense instead to shore up Trevenant's weaker stat, not bad for what you have.

How does PokeRadar work?

Beat both the 7th and 8th gyms with under-leveled Pokemon Lucario (39) being my star player for Drayden and Magnezone (39) with Thunder wave+Electro ball as my star for the last gym. Afterwards I caught Terrakion with a rash nature which it's not bad but not good either.

Does anyone remember the episode of Pokemon with the Scizor named Red lighting?

That's a perfect representation of a noob Pokemon player. SPAM ZE HYPER BEEMZ!