5 Runaway Steam-Kin Can Generate Three Mana For Every Three Spells Mana-generating creatures are always pretty useful, and Runaway Steam-Kin is an absolute powerhouse in red decks with plenty of cheap spells
He could play fewer, but he finds that he needs to combo off several times in many games, so he doesn't want to
Even without intending to, you'll quickly work out which cards aren't pulling their weight, and start seeking replacements
Thats the kind of question great game design always asks, which leads us to unearth the unearth mechanic
(Unless you're Ken Nagle, in which case you do it right to left.) However, there's an important distinction to make here: you need to see what you're actually going to want to cast at each mana cost, not what you can cast at each mana cost