Battle Moveset

A Good Moveset for Shiftry would have to be this:

Attacks:

Leech Seed
Toxic
Protect
Hidden Power Fire

Items Attached:

Leftovers

Preferred Nature:

Modest

Strategy Using Shiftry

HP Fire is here for something this moveset would fail against, and that would be steel types, which many cannot be effected by toxic. So if you ever come up against steel types, use HP Fire and this should help bring them down.
Although you can replace HP Fire with another move of your choice. This moveset is intended to deal damage slowly while you regain HP from Leech seed and Leftovers. Protect when you need too and want to gain an extra turn of leech seeding and your opponent losing HP from toxic.
For the natures, either a Special attack raising nature or speed raising nature will work well with this moveset. The EV's will also help this pokemon take more hits.
You can also try out this moveset too: Explosion/Sunny day/Solarbeam/HP Fire, a mixed sweeper that is often over looked, just change the EV's, nature and item it is holding to suite this moveset, and pick the ability Chlorophyll.
Choose Shiftry if you feel like using an under-used pokemon and choose whatever moveset you think will prove better in battles. Personally, I like the annoyer set but the Exploding one will work too.

EV Corner:

Max out the EVs in HP for Shiftry with any remaining in Special Attack & Special Defense

Strategy Against Shiftry

Shiftry's Defenses are both equally average. Your best bet here is to attack with it's weaknesses...Fire, Fighting Ice...they'll all work

Contest Moveset

A good Contest Moveset for Shiftry would have to be this for the Tough Contest best with Impish, Lax, Relaxed or Bold Nature:

Attacks:

Harden
Take Down
Bide
Pound

Items Attached:

Yellow Scarf

Strategy Using Shiftry

If you do the attacks in this following order you should have very few problems; 1st - Harden, 2nd - Take down, 3rd - Bide, 4th - Take down, 5th - Pound

Locations in Games

Ruby/Sapphire Evolve Nuzleaf Colosseum Trade from R/S Fire Red/Leaf Green Trade from R/S

Animé Appearences

Shiftry has had one Animé Appearence. It kidnapped Nurse Joy to take care of a wounded Nuzleaf and in doing so, aggrivates Brock who insists on helping get Nurse Joy Back. Episode 313: Jump For Joy! Episode 317: Treecko's New Technique! Watmel Field's Bullet Seed!