You may play that card for as long as it remains exiled, and mana of any type can be spent to cast it
Its definitely a card that you want to play on-curve, as drawing it in the late-game will just mean you have an overpriced Hordeling Outburst if you cant take advantage of casting a spell for free, which isnt much to write home about
Don't forget that making tokens is going to count, as this is not a cast trigger, unlike Karametra, nor is there a "nontoken" restriction written into the card
Especially the later sets, which arent shared too often
The first instant or sorcery spell you cast each turn costs (or ) less to cast for each land you control with a flood counter on it
Then you get to deal damage to each opponent equal to the number of tapped creatures the defending player controls