In low mana fights the main idea is to use your most mana efficient monsters. Usually this means using 1 tank and lots of small damage dealers behind the tank. To make those weaker monsters stronger we are looking at summoners that can provide a buff and make our smaller monster surprisingly strong. 2 summoners come to mind: Alric Stormbringer and Malric Inferno. However, sometimes Pyre is actually better than Malric, because attack speed is also very important in low mana fights, but more on that later.
The furious chicken and creeping ooze are 2 very nice cards to have to help you with low mana fights. Especially the chicken since thta's a 0 mana card. However, this card has become pretty expensive so I do understand that lots of you will not be able to use him.