It's one of 20 mythic rares in the set, which comprises 254 cards in total celebrating the twenty-five-year anniversary of Magic: The Gathering
(2017-07-14) If you cast a card "without paying its mana cost," you can't choose to cast it for any alternative costs, such as emerge costs
Why This Scene Box Stands Out
Number 9 Language English Legal Formats Brawl, Commander, Competitive Brawl, Historic, Legacy, Modern, Pioneer, Timeless, Vintage Not Legal Formats Alchemy, Pauper, Standard Rulings (6/15/2010) Training Grounds won't affect a cost that isn't the cost to activate a creature's activated ability
Primal Druid is the reason that the deck favors Wretched Gryff over Elder Deep-Fiend, as playing Gryff on turn 4 is so powerful for setting up Temur Emerge and building up a ton of resources while triggering Kozileks Return cheaply