Its hard to see when its unorganized.
Pokemon: 19
1x DialgaEX (PB)
2-2 Whirlipede (PS)
2-1 Toxicroak
3-2-2 Crobat (PS)
2-2 Ursaring (PB)
2x Kangaskhan (PB)
Too many different lines of pokemon. Definitely take out the Venipede/Whirlipedes if you dont have any 2nd steps. Its kinda of pointless. Take out Ursaring and Teddiursa, as they dont really bring much to this deck. Crobat and Toxicroak are both pretty good pokemon. Though they need something else to succeed. Dialga is also pretty pointless as well. Since it just requires you to add the metal and the plasma energy and doesn't bring much to the table. For Toxicroak could go 2-2 or 3-3 to have more consistency and it is still a pretty decent pokemon. Crobat should be like 3-1-3 or 4-1-4. Something like that. Try and shoot for 14-16 pokemon with a large amount of basics. Other strong basics you can add in for this deck is Giratina from PS, Mewtwo Ex, and Sigilyph with Safeguard. mr mime is also a possibility as it protects the frail Zubats. Can also try adding Lunatone, it allows you to look at the top 2 cards of your deck and rearrange them in any way you like and put them back. Then draw with night sight.
Supporters: 3
1x Skyla
2x Colress
Not enough supporters. You want at least like 10. 4 Professor Junipers, 3-4 Ns, and you can toss in the ones you have now. Maybe 1 more Skyla. Supporters are really important to decks as it allows you to draw more cards.
Trainers: 17
2x Ether (PS)
3x Hypnotoxic Laser
2x Virbank City Gym
2x Energy Retrieval
2x Great Ball
1x Scramble Switch Ace Spec
2x Potion
1x Switch
2x Pokemon Catcher
For this deck you probably want to get Rare candy as it will help you drop some middle steps like Golbat, making more deck space for other cards. If you are running Ethers i would suggest Pokedex also, as it allows you to rearrange the cards so that you can be sure an energy is the next card. Also with Crobats ability you can have Ether next, and then use night sight to draw it and then use it to attach energy.
Energy: 19
4x Double Colorless Energy
2x Plasma Energy
2x Metal Energy
11 Psychic Energy
Too much energy. But if you take out Dialga you can take out the 2 plasma and 2 metal, leaving you with 15 which is still kind of high. I built a similar deck before and it preformed well with 9 psychic and 3 DCE, though 4 is better. Probably dont go any higher than 13-14 energy.
If you adjust it in this way you can probably add a bunch more cards to this deck however you see fit. Though this is just my opinion. Having more than 2 lines of pokemon can cause consistency issues that can hurt your deck. Having more than like 14 energy can make you drown in energy with no other cards to play. Having not enough supporters is usually bad as well as supporters help speed up your deck.