Latias

Latias along with her twin Latios are not the powerhouse legendaries of this generation, and of the two Latias gets the short end of the stick. Having the inverse of Latios's Atk and Def stat means she's bulky and underpowered. She's built to take down gyms as a Dragon or Psychic-type sweeper but still can't compete with more common Pokemon like Dragonite or Espeon.

In the main series, Latias was given access to a Mega Evolution that will help patch up her weaknesses in generation 6, but when/if/how this is released is still a mystery.

Best PvE Offensive Moveset

• Dragon Breath is preferred over Zen Headbutt for yielding higher cycle DPS and being much more dodge-friendly.
• Charm doesn't have much use on Latias, especially without STAB. 
• Outrage is the preferred charge move. It partially makes up for Latias's lower Atk compared to Latios.
• Psychic has synergy with Zen Headbutt and makes Latias a somewhat tanky Psychic attacker.
• Mist Ball* is Latias' signature move, but it's ultimately inferior to Psychic.
• Thunder is sub-par move. TM this move.

A PVP staple, Dragon Breath has high damage output and average energy generation, meaning it's definitely Latias' best quick-move. Outrage is a good attack in PVP, with a higher damage-per-energy ratio than the famed Dragon Claw. However, it takes nearly twice as long to charge, meaning it functions best as a closer move while the later is best for shield-shredding. Thunder and Psychic are weaker than Outrage, but they give Latias much needed coverage.

Charm is a very hard-hitting move that's completely unique to Latias among Dragon-types, but it emphasizes its issue of only having slow charged moves by generating energy at an extremely low rate. It can come as a surprise to opponents, though it doesn't really change Latias' already positive matchups against Fighting and the neutral ones against other Dragons.