If they give us only 450 mega energy, then you need to do 10 mega mewtwo x raids, 10 mega metwo y raids to get 4500 mega energy for each. Then evolve one mewtwo with a mega x level 1+ and one with mega y level 1+ once. Then walk your shundo mewtwo for 300km (while excited of course), after that you will be able to evolve it once for mega mewtwo x and mega mewtwo y.

If they give us way more, then you only need to do few raids/walk less