What could you do with Fiends that are fierce and going to your gate and at the same time you don't have much mana and you have to defend the whole map so you could stop these fiends from going to the gate and cost you more hearts and this is the point here.
When you have low mana first option to think about is common towers as in this case rare and epic towers would be so expensive to use and you wouldn't have such ability to use these towers as least one is more than 100 Mana.
Even some common towers couldn't be used as you are to use a towers that less than 100 Mana and these are such Card Sharp and also fountain of terror and this is a two towers to use for moderate mana to be used.
