For a quick investment of 3 mana, you acquire a 3/3 with trample
Since a relatively pure Train Deck is heavily geared towards going second, the Deck's gameplan can be often derailed when going first due to the limited interactions the Deck can put up against the opponent, with the typical "end board" only consisting of a single Rank 10 interruption ("Super Dora" / "Gustav Rocket" / "Varudras")
Of course, it's hard to imagine a Charizard card would stay cheap forever, especially paired with a likable trainer, like Leon
Dont forget he can move an attached Aura
By reducing Yu-Gi-Oh down, Duel Links has removed one of the game largest barriers to entry
Live Twins also help out the Sprights by being level two monsters on the board that fulfill the requirement needed to start spamming out Sprights from the hand