Gaddock Teeg
Legendary Creature — Kithkin Advisor
Noncreature spells with mana value 4 or greater can't be cast.
Noncreature spells with 
in their mana costs can't be cast.
So great are his wisdom and spirit that many who have met him say that they stood before a giant of a man and talked to the wisest of the four winds.
Greg Staples
Ultimate Masters (UMA)
• #199Rulings
A spell's mana value is determined only by its mana cost. Alternative costs (including casting a spell "without paying its mana cost"), additional costs, and cost reductions don't affect a spell's mana value.
(wotc • 2018-12-07)
If one half of a split card has a mana value of 3 or less and doesn't have an {X} in its mana cost, Gaddock Teeg lets you cast that half.
(wotc • 2007-10-01)
Rulings
A spell's mana value is determined only by its mana cost. Alternative costs (including casting a spell "without paying its mana cost"), additional costs, and cost reductions don't affect a spell's mana value.
(wotc • 2018-12-07)
If one half of a split card has a mana value of 3 or less and doesn't have an {X} in its mana cost, Gaddock Teeg lets you cast that half.
(wotc • 2007-10-01)