Battle Moveset

A Good Moveset for Yanma would have to be this:

Attacks:

Endure/Substitute
Reversal
Shadow Ball
Hidden Power [Flying]/Aerial Ace | Psychic

Items Attached:

Liechi Berry

Preferred Ability:

Speed Boost

Preferred Nature:

Lonely or Adamant

Strategy Using Yanma

This about the only decent set of Yanma. Substitute or Endure activates the Liechi berry and gets Reversal at maximum power while in the mean time it gives times for Speed Boost to kick in, making you faster than all opposition. Shadow Ball covers the resistant/immune Ghosts and Psychics and Hidden Power Flying/Aerial Ace cover resist Bugs while maintaining STAB. The major advantage of Endure > Substitute is that Yanma can switch out and come back in at a later stage and still be guarantied at least one speed boost to outrun whatever opponent is in play (it'll outrun all un-boosted opponent's short of Ninjask, Electrode and Deoxys).

Psychic is an odd choice but can work to some extent, since a Yanma's Psychic will 2KO most Poison types not named Muk or Vileplume.

[Just a word of advice, don't try to use a Reversalling Yanma in OU. Tyranitar's Sandstorm will KO it and Yanma will be completely stomped on by the majority of physical walls.]

EV Corner:

With Psychic:

EVs: 252 Atk / 156 Spd / 102 SAtk
Lonely Nature (+Atk, -Def)

The lost Speed is not an issue since Yanma can easily afford to spare the EVs into Special Attack while maintaining a 264 Speed.

Without Psychic:

EVs: 252 Atk / 252 Spd / 6 SDef
Adamant Nature (+Atk, -SAtk)

You may as well max out Speed for a better chance of outrunning Electrodes and Ninjasks. The 6 EVs leftover can go anywhere really, just as long as it doesn't bump up your HP stat so that it's divisible by 4 (for Sub users).

Other Optional Sets:

Yanma @ (No Item)/Leftovers
Trait: Compoundeyes
EVs: 6 HP / 252 Atk / 252 Spd
Jolly Nature (+Spd, -SAtk)
- Hypnosis
- Signal Beam
- Hidden Power [Flying]/Aerial Ace
- Thief/Screech

Put something to sleep with your 80% accurate Hypnosis, steal something's item (Choice Band would help out here) and then attack with your two STABs. Hypnosis should disable something for multiple turns so once that's hit you've at least accomplished something. Stealing an opponent's item always causes problems and if you manage to do some damage with your offence you've accomplished quite a bit, since this Yanma has the potential to cripple a couple of Pokémon as well as do some damage. You could also go with the Screech approach rather than stealing an item, increasing your potential to KO something (but decrease your likelihood of crippling an opponent's Pokémon).

Yanma @ Choice Band
Trait: Compoundeyes/Speed Boost
EVs: 6 HP / 252 Atk / 252 Spd
Adamant Nature (+Atk, -SAtk)
- Shadow Ball
- Signal Beam
- Hidden Power [Flying]/Aerial Ace
- Hypnosis/Quick Attack/Mimic/Steel Wing/Hidden Power [Ground or Rock]/Reversal

Yanma has a decent number of physical moves and two physical STABs so CB-Yanma gets a mention. If you use Hypnosis go with Compound Eyes, otherwise go with Speed Boost. You've got CB Quick Attack for picking off injured Pokémon, Mimic for copying an Earthquake (or something), Steel Wing so that you can use Hidden Power [Flying], Hidden Power [Ground or Rock] for the offensive diversity and Reversal if you expect to find yourself low on HP (and you probably will if you don't get KOed one none hit).

Strategy Against Yanma

Physical walls (not weak to Reversal, Flying or Ghost attacks) shut the Reversal Set down pretty much, although Weezings and other Poisons should watch out for what can be a 2KO from Psychic.Quick Attack (etc) also shut down the Reversal set however Yanma always retains the ability to switch out and come back again and still destroy the Base 130 (Speed) Pokémon, due to Speed Boost. Tyranitar's Sandstorm is a guarantied KO as well since Sandstorm damage will pick off it's last remaining point of HP.

Fast Substitutes stop Yanma sets using Hypnosis as well as Insomnia/Vital Spirit Pokémon, although it can usually catch people off guard when it uses Hypnosis (since everyone expects the most effective set, the Reversal set.) and a lot of the Pokémon immune to sleep attack are weak to one of Yanma's attacks

. Yanma gets to join Weedle and Caterpie on the list of most fragile Pokémon as well, since it's very mediocre defences will get destroyed by pretty much anything using attacks that aren't 'Not very Effective'.

Contest Moveset

A good Contest Moveset for Yanma would have to be this for the Smart Contest best with Calm, Gentle, Careful, Sassy Nature:

Attacks:

Tackle
Shadow ball
Psychic
Aerial ace

Items Attached:

Green Scarf

Strategy Using Yanma

If you do the attacks in this following order you should have very few problems; 1st - Tackle, 2nd - Aerial ace, 3rd - Shadow ball, 4th - Psychic, 5th - Aerial ace

Locations in Games

Ruby/Sapphire/Emerald Trade from FRLGC Colosseum Snagged from Cipher Peon Nore in Pyrite Hill Fire Red/Leaf Green Ruin Valley

Animé Appearences

Yanma has had a few Animé Appearences. First it was breaking all the windows in town. After that Forrester used it in his Double battle against Ash and after that it was used by a trainer in the PokéRinger contest Episode 179: Wings 'n' Things! Episode 290: All In A Day's Wurmple! Episode 356: That's Just Swellow!