4 Ponyta LV
Otherwise you start the infinite loop that ends in their defeat when you hit combat damage with the Starscape Cleric, or my personal favorite, put a dirt cheap dual land, Scoured Barrens or Forlorn Flats into play
Both are worth playing in decks that support them as ways to cheat high mana costs on exceptional threats like Bolas's Citadel and Atraxa, Grand Unifier
It's a rarer situation, but Mind Flayer is probably one of the most potent answers to a Grenzo, Dungeon deck that likes to play things from the bottom of its library
Colorless mana was, and remains, confusing
Before you ever consider common or uncommon specs, consider your options in mythics, and then rares where you can cycle fewer sales for bigger profits per sale, reducing your time spent per transaction and lowering your incidental transaction costs such as shipping and materials