This became salientized in card-play because of having an established rule-set and, increasingly, the growing industrialization of card-making
Talrand, Sky Summoner This legendary Merfolk Wizard hails from the core set Magic 2013, and it has long been a favorite for spellslinging Commander decks
Once I landed (pun intended) on that, I won five games in a row, before succumbing to the strongest thing in Limited since the dawn of Magic: an uncontested flyer
There are other things to consider, like rarity, but those are the big factors you need to consider when making custom cards
You could always play Sheoldred to get a similar effect, a big body that snowballs if you untap with it
The Ninja card stays revealed and isn't put onto the battlefield until the ability resolves