Humble Naturalist — ruling 1

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.

Humble Naturalist : règles, fonctionnement et interactions (MTG)

Humble Naturalist is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

: Add one mana of any color. Spend this mana only to cast a creature spell.

How it works : Humble Naturalist

Original English text — Wizards of the Coast / Scryfall

#1April 17, 2020· Wizards of the Coast
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.
No other card is named in this ruling.