Mana produced by Humble Naturalist can be spent on any part of a creature spell’s total cost, including additional costs (such as kicker costs) and alternative costs (such as mutate costs). It can’t be spent to pay the costs of abilities of creatures you control.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.