The first tier has already been surpassed, which includes the Containment expansion for Defense Grid: The Awakening and a digital art book. Tier 2 includes Awakening, the Containment expansion and a 50 percent off coupon for Windborne, Hidden Path's sandbox adventure game that's currently on Early Access. That leaves tier 3, which is dedicated to A Matter of Endurance, an "original audio story" to be penned by Mary Robinette Kowal that will arrive "on or before" Defense Grid 2's launch.
There's also the special edition, which offers a second digital art book dedicated to Defense Grid 2 and The Making of Defense Grid 2: The Complete Story Behind The Game, an e-book by Russ Pitts. Special editions will also include the content from every tier that's unlocked through accumulative pre-orders.
Anyone that chips into the pre-order pool will save 10 percent from Defense Grid 2's eventual launch price, meaning standard pre-orders are currently $22.49, with special editions going for $26.99. Pre-ordering will also grant "immediate access" to Defense Grid 2's Windows-only beta, though Mac and Linux users (as well as Xbox One and PS4 owners) are welcome to build trails of death in the finished version.