While all three of the Kanto starters in the game possess strong Pokemon Powers that allow players to manipulate energy, only Rain Dance allows for strong energy acceleration: being able to rapidly bring energy cards into play
You can copy big, flashy spells like Crackle with Power, Expropriate, and Aminatou's Augury to throw yourself well ahead of your opponents or lean into the combo side of things
However, Calyrex is not your only attacker, and this flexibility is what makes the strategy shine
Since the Water Shuriken is only available on Greninja, a Stage 2 Pokmon, you will need its pre-evolved forms to come out as fast as possible
And why the games were designed in the way that they were, so that people could interact with one another, you know, be able to trade or to battle or just, you know, to talk