Having access to it every game, at all points of the game, makes your deck incredibly resilient and strong
Akroma, Angel of Fury Akroma, Angel of Wrath Animar, Soul of Elements Azusa, Lost but Seeking Bident of Thassa Brion Stoutarm Darien, King of Kjeldor Gisela, Blade of Goldnight Grenzo, Dungeon Warden Hanna, Ship's Navigator Ihsan's Shade Iwamori of the Open Fist Jace, the Mind Sculptor Jalira, Master Polymorphist Kongming, "Sleeping Dragon" Mikokoro, Center of the Sea Nicol Bolas Niv-Mizzet, the Firemind Pendelhaven Prossh, Skyraider of Kher Ruric Thar, the Unbowed Stangg Thalia, Guardian of Thraben Vendilion Clique Zada, Hedron Grinder
This is for two reasons: the opponent can kill the Foundry to get a 2-for-1, and it costs too much mana
Heliod, Sun-Crowned goes infinite with any number of cards across formats: And that isnt counting the large number of 3-card combos
Unofficial set symbols