I thought of a nice deck with Latios EX c;
Latios/Sigilyph/Cofagrigus
Pokemon: 7
2 Latios EX
3 Sigilyph (Safeguard)
1-1 Cofagrigus (Six feet under ability)
Strategy with Pokemon: Sigilyph will be T1 Active Pokemon, so it can give you a couple of turns to get away with setting up the attack Luster Purge with Latios EX. Latios' attack Luster Purge will do 150 damage, but discarding all the energy attached to Latios. The attack isn't enough to knock out most EX Pokemon, so by the time you'll be at T3 with the set up Latios you will most likely have Cofagrigus out as well with its ability 'Six Feet Under' to deal that remaining 20 or 30 health points for the EX knock out.
Energy: 14
9 Psychic
5 Water
Strategy with Energy: You will need a consistent amount of both Psychic and Water energy to set up Luser Purge with Latios. If you are up against a deck that Latios has a disadvantage, then use Sigilyph as an alternate attacker with maximum only one Water energy and two Psychic energy for its attack.
Trainers: Supporters
4 N
4 Juniper
3 Skyla
2 Colress
2 Ghetsis
15
Strategy with Supporters: A consistent supporter count because you cannot waste a single turn without attaching energy and benching Latios, Sigilyph, and Cofagrigus.
Items and Stadium:
3 Pokemon Catcher
3 Ultra Ball
3 Bicycle (Extremely mandatory since most cards are not dead in the hand!)
4 Hypnotoxic Laser
3 Switch
3 Enhanced Hammer
1 Max Potion (Incredible after Latios' attack Luster Purge, but only one not to break the consistency of the deck.)
1 Super Rod (Late game third Latios, Psychic, and Water energy.)
1 Float Stone (Latios' retreat cost is somewhat heavy and cannot lose previous energy attachments.)
1 Virbank City Gym
ACE SPEC: LIFE DEW (Mandatory!)
Ace Spec strategy: Life Dew late game or using attaching with Cofagrigus' ability 'Six Feet Under' works miracles during the game, so I won't say much since it's self-explanatory.
The deck has been tested and I have an equal Win/Loss ratio, so the deck is pretty fine how it is. However, there's another deck idea that I don't own that's called Latios/Blastoise, but I feel as if this deck is much better for Latios EX in my opinion.