Fires of Invention
Oracle Text
You can cast spells only during your turn and you can cast no more than two spells each turn.
You may cast spells with converted mana cost less than or equal to the number of lands you control without paying their mana costs.
First, it's only 4 mana. They like to put big effects like this on 6cc cards. Sunbird's Invocation Mirror March Things like that.
Second, it's not color limited. It only has one Red mana in the cost which means it doesn't need a mono-Red shell. Further, I'd expect it to have a color limitation. Either, only gives you free Red spells or only let you cast things you could pay for.
Unless decks are playing a lot of enchantment hate, I can see this card being very good.