Zarude

Zarude

But first, what do we already know?

Typing - Dark/Grass
Bad defensively, we can all agree. And yes U-Turn will be a big problem, but it's not the death of a pokemon, just switch out!
(Also First Impression though...)
At least offensively it can put a lot of pressure on

Ability - Leaf Guard
Not good, even if it was defensive and had better typing this ability is too situational.

Moves - Power Whip, Taunt
Good, hopefully physical attacker, Taunt could be neat if fast

HP stat - 212 at level 60
After checking many previous pokemon reveals, most do not have EVs, and have a random amount of IVs (usually around 21 IVs).
What does this mean? Base HP stat of 105. It's high, but that may not actually be a good thing and I will go into why...

So what are 3 things that could make this Pokemon good?

1. Stats - Most important
As with most mythicals, like BST of 600 which is great, but has to be distributed well.
HP	- 105: locked in
Atk	- 164
Def	- 75
SpA	- 65
SpD	- 75
Spe	- 116

Seeing as though HP is locked in, we need an offensive spread like Darmanitan: high HP, low defenses and SpA, very high attack and good Speed. Darmanitan is a good comparison as it also has bad defensive typings, but is very powerful and relevant!

2. Moves
Power Whip is great
Knock Off would be amazing
Sucker Punch also would be very important
Gunk Shot for fairies - seen with both Infernape and Simisage
Close Combat, HJK or even Cross Chop

U-Turn - maybe its biggest fear, but its greatest weapon
Parting Shot

Swords Dance
Hone Claws - increase power and accuracy with Power Whip/Gunk Shot/Cross Chop
Could even get Hypnosis with eyes like that or maybe Sleep Powder/Grasswhistle
NOT SPORE - in Japanese this translates to Mushroom Spore, therefore only mushroom Pokemon get this

3. Hidden Ability
VERY unlikely - all mythicals so far have only 1 ability, even ones with multiple forms.
If it could, Tough Claws would immediately be p cool, it would boost the power of Knock Off, CC, U-Turn.
Adaptability would also be great and would seem to make sense - it has great offensive typing to abuse, and it seems like a very adaptable fighter with its extendable vines.
OR instead maybe speed boost as it swings through trees and runs about?

BUt we're probably stuck with Leaf Guard...