Nice card, but I'd change the costs; the casting cost is too cheap, IMO. The unupgraded spitfire is equal to the unupgraged horned frog, -plus- it has another ability, so I'd make the unupgraded Spitfire cost 3
, leaving the adrenaline cost the same. The Elder Spitfire costs the same as the Lava Destroyer, which is one of the most powerful creatures in the game, and the Elder Spitfire is arguably similar or even stronger; certainly stronger to begin with. I'd increase the upped cost by 1 as well, maybe even 2. If it were any other two elements, even that might be too cheap, but life has the most quanta efficient creatures, and fire the next most, so it is reasonable that a fire/life hybrid card is cheaper than it would be in another pairing.