There are monsters costs 1 mana , there are ones cost 14 mana and there are monsters which costs nothing to use. As you know in low mana battles using monsters which cost 0 mana can change the outcome of the gane significantly therefore if you don't have 0 mana monsters then enemy will have huge advantage over you. Scorch Fiend is one of the best legendary 0 mana monster. If you use it at max level then he will reduce enemy's melee attacks -1. This card is such na beast if u use it at low mana battles with equalizer game mode on. Other than equalizer this card will be good in every low mana battle in my opinion. Because it cost 0 mana even at level 1 using this card can change the outcome of the battle.
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From @mozila