The goal with Mages is to reach a powerful late game build that deals extremely high AoE magic damage. A great aspect of the Mage bonus is that it amplifies the magic damage dealt by non-Mage heroes as well, which means that good late-game units with powerful AoE spells have great synergy with Mages.

Mages are a level-value strategy. This means it's better to invest in experience rather than rolls. Mages don't benefit from low-tier three-star heroes too-much, but they work great with 4 and 5-cost heroes, so reaching lvl10 plays a big role in your in getting close to the builds power-cap.

The key heroes in a Mage build are the Human Mages because they allow you to get the key for the strategy (4) Human mana generation bonus easily. Moreover, a two-star Keeper of the Light is one of the key carries of a Mage build.

The Primordial Mages are also quite Important - in our late game Underlords builds test Mages and Primordials were pretty much the best Alliance combo for late-game strength.