Though Latios isn't the best on the physical side, it's somewhat usable. In its mega form, it's very good! Here's a recommended moveset for your mixed Latios:
Latios@Latiosite
EVs: 252 Attack, 100 Special Attack, 156 Speed
Moveset:
Steel Wing (Coverage, especially against Ice, Fairy, and Rock)
Draco Meteor/Dragon Pulse (STAB. I recommend Dragon pulse, since it doesn't lower your Special Attack)
Zen Headbutt (STAB. Has a flinch chance and good power)
Dragon Dance/Earthquake (Either raise your stats or dish out hits)