Mewtwo+Mew EX

CALCIUM Sorry for seeing your comment really late, but this deck doesn't really have much synergy or really lets Mewto function at all. If you read Team Rocket's Mewtwo ex (Destined Rivals) ability, it says that it cannot attack unless you have 4 or more TR's Pokémon in play. Also, you have way too much Energy, you should cut your Grass Energy and Pokémon out entirely or make it 4 if you add in TR's Spidops to synergize with Mewtwo which is needed to attack with. Also, you should add in Lillie's Clefairy ex and if you don't want to add in the TR's Pokémon, you can replace the Mewtwo ex that won't work with the Tera Lightning/Electric in Pokémon Mewtwo ex since it has better Synergy with Mew ex. Furthermore, your Mew count is a bit too high so I'd suggest making it go down to 2 since you focus on Mew and Mewtwo. Additionally, Rare Candy is useless in this deck along with Poffin. You should also probably remove Giovanni's Charisma and Artazon. Now for cards you could add are 1 Counter Catcher, a 4th Nest Ball, 2 Earthen Vessel's, 2-2 TR's Spidops Line, 1 TR's Articuno, 1 Lillie's Clefairy, 4 TR's Energy, 1 TR's Murkrow, and the other TR Supporter Cards and some of their item cards but if you decide to use the Tera Mewtwo instead, run 2 Tera Mewtwo's, 1 Lillie's Clef, 4th Nest Ball, 1 Counter Catcher, 2 Vessels, 2 Pokégears, 2 Area Zero Underpdepths, 2-2 Xatu Line, and you need an ACE SPEC so choose Prime Catcher or Secret Box. Hope this helps!

CALCIUM Oh right also forgot to mention to also add in 2 Bravery Charms.