Externally, the archetype has good synergy with the "P.U.N.K." archetype, which requires paying LP to activate their effects (thereby enabling the effects of "Gold Pride" monsters) and synergizes with the Deck's use of Synchro Summoning
Legality depends on the tournament format -- The Duke of Demise can be legal in some formats and banned or restricted in others
Aside from those situations, though, Mewtwo EX and Gardevoir can stomp almost everything which comes at it: you can get to take advantage of Psychics massive power without the slow, plodding build-up
In an Eternal format like Commander, players have access to so many cards that you can take an otherwise basic mechanic (like gaining life) and turn it into so much more
Fairy: You can draw 3 cards, then place 2 cards from your hand on the bottom of your Deck in any order
Furthermore, the game's price is far more reasonable for players than games like Yu-Gi-Oh and Magic the Gathering, because the best deck in the format is only about $100 unless players look for alternate art copies of the cards they need