This is a good way to Catch opponents off guard, Dual screen Latias:
Latias (F) @ Light Clay
EVs: 204 HP / 32 Def / 4 SAtk / 16 SDef / 252 Spd
Bold Nature (+Def, -Atk), Timid Nature (+Spd, -Atk)
- Dragon Pulse / Mist Ball / Psychic
- Wish / Recover
- Light Screen
This is actually one of the faster and best dual screeners in the game, but it is often over shadowed due to it's offensive prowess.
First move is preference, I prefer Dragon Pulse, simply because it hits more neutral. Mist Ball has the defensive boost, while Psychic has an offensive boost, all benefit from STAB. The second move is also preference, both are recovery, Wish takes a turn, but it can be used to heal an ally, while Recover is instant, and a little more selfish.
Light Clay + Screens are the only way to go, in my opinion. Leftovers is plausible, as is Lum Berry, but Light Clay just adds to the utility of Latias.
EVs and nature aren't difficult, Speed gets the screens up before attacks come flying at it. HP EVs are to make to defense boosts worth using, while defensive EVs are to keep it bulky and annoying. Offensive EVs aren't needed, as Latias has only one attack. Nature is easy, either something to boost Def, it's lower stat, or Speed, to help with screens.