Earning & Spending Diamonds
Diamonds are the most important currency in the game. They’re much harder to obtain than any other, so spend them wisely.
Your main source of this will come from completing campaign quests. The quests are basically achievements for completing certain things in the game such as defeating campaign stages or king’s tower floors.
As you progress further into the game, your sources of diamonds will slowly deplete as campaign quests can only be completed once.
The Arena of Heroes can also give diamonds as daily and seasonal rewards depending on your ladder position.
And lastly, you can buy them with real money from the gift shop.
There’s 2 main things you can spend diamonds on; Heroes and Gear. You can also use them for resetting heroes, but the cost is relatively low (20 per hero).
So which one is the best? This can depend on what your current progress in the game is, but the general answer for most players is to spend them all on buying heroes from the library.
The logic behind that is while you can buy decent gear from the store, the only gear you should really consider buying from it is Mythic tier.
That’s because as you progress further into the game, epic and legendary gear can be acquired relatively easily from a multitude of other sources such as the Peaks of Time, AFK Rewards and the Guild Store.
You also only really need gear for 5 heroes, but you’ll need A LOT of extra heroes to ascend them into Mythic+.