Nice! A solid advantage; and a built in limit to stop you going infinite - making it a card for people who want to play the game rather than fire of ridiculous combos... and those combo people will just take it as an extra challenge :)

Of course "Not infinite; but I have 30 mana and all my cards to choose from" is pretty game winning on its own. But so is the more normal usage of "I just cast four 1-drop elves, for free, and they cantrip now."

Very nice. Needs a theme, may I suggest a hydra? They are allegedly green's big beasty, and we almost never see any.

The one tiny niggle is that it's 7 mana, and 6/6. Round numbers would be nicer; but I think I agree with the costing and size you have here, mechanically.

This is quite a lot more powerful than Recycle/Null Profusion, and even miles better than Commander staple Primordial Sage.

Those are good points. Make it an 8 mana 8/8; for the roundness of the numbers. Then make it mythic; because that basically removes all "It's too powerful" complaints. :(

I like those suggestions. I recently started playing a Yidris EDH deck, and one thing I noticed is I cast a /lot/ of spells each turn, and was thinking "what's a way to get value off the fact I'm doing this" (besides Storm), so that is sorta the idea behind the design here. EDH Storm decks or something.