During many of your battles, you may see the option to Borrow a Hero.

Borrowing a hero is exactly as it sounds! You can borrow another player’s unit for the duration of the battle and use it as one of your own. Once the battle ends, the hero is no longer in your party or collection. 

Alongside gaining additional power for the upcoming battle, you will also be rewarded with Ally Points. The amount of points earned can differ depending on the hero you choose, which can then be spent to open Bronzium Data Cards in the store and on items in Weekly Shipments.