Nico Nico Nii!~
I guess those could work, but what makes Mewtwo EX lethal is its X-Ball attack, so that'd really only leave them as being effective for Sigilyph, which does need Psychic Energy to attack.
You might also still encounter some speed issues trying to set up your Stage 2 Pokemon, since most decks you'll be facing will be using big Basic EX Pokemon, and with Pokemon Catcher around, they'll likely "Catcher" up your Basic that evolves into your Stage 2 you're trying to get into play. Maybe drop the 2 Giant Capes for 2 more Professor Juniper or for 2 more Great Ball (Ultra Ball would be preferable to Great Ball if you have any). I'd drop an Escape Rope or 2 as well in favor of 1 or 2 more Skyla.