I want to say this early on, because it took me a while to realize that I was missing out on some very important boosts during the battles. And that is attacking with heroes that color match the tiles on the field. Each time you tap a tile (or crystal or whatever) to reveal what's behind it, the color of the other diamonds changes. In battle, this means that if you attack with a character of the same color (aka element), that hero will get a boost in damage when attacking, but they will also recover health and mana. For example, if the crystals are green and you're attacking with a nature element hero (which are the green heroes), you will get the benefits. This is something extremely important to know, as it helps you make better choices in battle.