Mienshao, without a doubt.
Here's why:
Meowstic's attack is terrible, period. It is meant to be a Special attacker, so Fake Out just doesn't serve any purpose, except to stall a turn, at pathetically low damage. Further, your's is Timid nature, so the attack is down by another 10%. It just doesn't make sense at all!
Mienshao's attack is good, and can use Fake Out in a much, much better way. This is because, by using U-turn, the next time you send out Mienshao, it can still use Fake Out! That's right, you can re-usse Fake Out time and again, something that Meowstic without Regenerator is too weak to pull off!
Here's the moveset you might want to try out:
Mienshao @ Wide Lens < Life Orb
Ability: Regenerator
Nature: Jolly
252 Atk/4 SpD/ 252 Spe
- High Jump Kick (STAB, with Wide Lens its less likely to miss)
- Poison Jab (For Fairies) << Fake Out
- U-turn (In case High Jump Kick misses and need Regenerator activated)
- Knock Off (Willing to replace for Fake Out) (For Psychic types as well) ----> Keep this!
Now, this is because if you're up against a Fairy type, your best bet is to switch out using U-turn as opposed to staying in. This makes good use of the ability as well! Further, you need Knock off to deal with Ghost types, and its side effect is a massive advantage in competitive battling!
Life Orb damage is covered by U-turn activating your ablity, so you don't need to worry about that. Further, the 30% boost is very useful in KO-ing some of the more defensive 'mons out there.
Other than that, good luck with the challenge! It sounds interesting, and I hope you win! Also, don't worry about the missing tags. Once you're at 80 points or so, you can create your own tags. Besides, they're mainly to help editors keep things organized, and with the currents tags, you're not too off with respect to your question, so in this case it shouldn't be too much of a problem.
