Jodah, Archmage Eternal — ruling 1

Jodah's ability is an alternative cost to cast a spell. You can't combine this with other alternative costs, such as flashback. You can pay additional costs, such as kicker, in addition to this alternative cost.

Jodah, Archmage Eternal — ruling 2

If you apply Jodah's alternative cost to a spell with {X} in its mana cost, X is 0.

Jodah, Archmage Eternal — ruling 3

If you cast a spell for which mana may be spent as though it were mana of any color, you may cast it for Jodah's alternative cost and still spend mana as though it were mana of any color.

Jodah, Archmage Eternal : règles, fonctionnement et interactions (MTG)

Jodah, Archmage Eternal 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

Flying You may pay rather than pay the mana cost for spells you cast.

How it works : Jodah, Archmage Eternal

Original English text — Wizards of the Coast / Scryfall

#1April 27, 2018· Wizards of the Coast
Jodah's ability is an alternative cost to cast a spell. You can't combine this with other alternative costs, such as flashback. You can pay additional costs, such as kicker, in addition to this alternative cost.
No other card is named in this ruling.
#2April 27, 2018· Wizards of the Coast
If you apply Jodah's alternative cost to a spell with in its mana cost, X is 0.
No other card is named in this ruling.
#3April 27, 2018· Wizards of the Coast
If you cast a spell for which mana may be spent as though it were mana of any color, you may cast it for Jodah's alternative cost and still spend mana as though it were mana of any color.
No other card is named in this ruling.