If you cast a spell for another cost "without paying its mana cost," you can't choose to cast it for any alternative costs
Ancient Silver Dragon Body of Knowledge Choice of Fortunes Chronatog Avatar Curiosity Crafter Decanter of Endless Water Enter the Infinite Finale of Revelation Graceful Adept Kruphix, God of Horizons Library of Leng Marina Vendrell's Grimoire Mordenkainen Morska, Undersea Sleuth Ms
The first edition stamp also differentiates it from other printings of this card
However, these days many fakes can pass the light test, which makes it extremely unhelpful when you're already unsure about a card
About the only thing that'd make this card better would be somehow giving all those Dragon Elementals haste
Now the rest of the table has to quake in fear, wondering what that player is going to do with the eight mana he or she has available on their second turn (assuming a second land drop)