The Brothers' War features prototype cards, which have a mechanic that represents an artificer's work in different stages of development. Each prototype card is an artifact creature which has a secondary set of mana cost, power, and toughness characteristics that are inset in the top of its text box. It can be cast using either its normal characteristics or it can be cast as a smaller "prototyped" version of itself that uses the secondary characteristics instead.

Casting powerful spells is great, but sometimes excavating the past can be just as useful. Unearth is a returning mechanic that lets some permanent cards return to the battlefield one last time. Previously, unearth has appeared mostly on creature cards, but The Brothers' War features the mechanic on some artifact cards too.

The first time in a game you control a permanent with start your engines!, your speed becomes 1. This happens immediately, so no one can respond and try to remove the permanent before you pick up speed. Once your speed is 1 or greater, you can trigger an ability to increase your speed. That ability is "Whenever one or more opponents lose life during your turn, if your speed is less than 4, increase your speed by 1. This ability triggers only once each turn." This ability isn't tied to any permanent. For the rest of the game, it can be triggered as long as your speed is less than 4, no matter what permanents you control.