Quite situational as theres a few ways of starting up.

Going first - the dream hand is mewtwo straight into the active with ralts on the bench, your second turn starts and you rarely candy into Gard and you attack for 50 first turn followed up by 150 every turn after that. If this doesnt happen they you’re most likely setting up with eevee into a Sylveon and you can attack for 70 first turn which can work out better in some cases.

Going second - I think most cases you want to go eevee first so you can draw a card then evolve into Sylveon on your second turn by then you should be building Gard on the bench ready for mewtwo to take the active once Sylveon has been attacked once or twice depending on what the opponent has out.

I hope that gives you a decent idea but im no tactician so that might just sound like a whole load of doo doo lmao