I have a feeling that this deck may be seeing some consistency issues since almost one third of your deck is Energy. I think that you can safely cut down your Metal Energy count, maybe drop it down to about 3 basic metal as opposed to 6.
-3 Basic Metal
With those three extra spaces, I would try to increase some of your trainer staple lines.
+1 Pokémon Collector
+2 Professor Oak's New Theory.
This should help your decks overall consistency, a turn one Collector is always nice, and the ability to refresh your hand on a regular basis is a must. While I am suggesting way to improve the decks overall consistency, you might want to try this out as well.
- 2 Defender
+2 Junk Arm
Junk Arm is a beautiful staple that can allow you to recover many critical cards in your deck, such as Pokémon recovery, search, and healing power. I see no solid reason as to why it shouldn't be maxed. I find Defender kinda pointless in this deck, so I figured you could live if you dropped it. Correct me if I am wrong, but I see nothing in the format that is going to one shot you except Reshiram, which Defender does nothing against anyways. With a base 130 HP, special Metal Energy and Eviolite are going to be more than enough damage reduction power.
If you are looking for healing power, I don't think that Moo Moo Milk and Potion are going to be the best cards you can play. I would suggest that you run Max Potion; however, I don't think that Cobalion is going to be able to handle the potentially massive energy loss after the healing, and Shaymin is a waste of time. I think the best way to heal damage off of Cobalion would probably be
Life Herb. The coin flip is going to be stressful and a great risk, but I think the extra healing power is well worth it. Plus, with 3 Life Herbs, and a playset of Junk Arm, you should be able to play more than one per turn if need be.
-2 Moo Moo Milk
-1 Potion
+3 Life Herb.
I'm hoping that these suggestions help. Ok.