Delighted Halfling One of the best mana dorks ever printed, Delighted Halfling is legal in Historic
For example, if you have mostly Fire-type Pokmon, you'll want to have mostly Fire energy cards in your deck
Think about the typical journey of a Magic player: they start off playing casually, at home on the kitchen table with friends, and slowly work up the ranks of competitive play, going to FNMs, Game Days, and perhaps eventually Grands Prix and so forth
Using these kinds of dual purpose cards will allow you to increase certain interactive and disruptive components of your build without hitting the engine consistency
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It sees extensive play in every format where its legal