I agree with this list, with perhaps the exception of Efreet Elder - I have not had much luck with him, though any card can of course be useful under the right conditions. In the lower leagues fire is probably best for low mana battles - with Cerberus and spy carrying the whole team. But what really helps is having a chicken and and ooze as well to absorb some shots with sneak/opportunity in these low levels and give another speed boost. Even in a 17 mana battle I sometimes switch to the lava as it hast to be one of the best early tanks in the game. Only other card with a mention is Kobold Miner. Not as strong as the spy, but not bad to fill out a low mana team.