In Commander Keen 9: Battle of the Brains, eight-year-old genius Billy Blaze pulls out his pogo stick and raygun for one last desperate run across four alien worlds. Built on a heavily patched engine, this massive fan creation closes out the unofficial trilogy with some of the toughest platforming in the series.
How Ceilick built a full sequel out of MS-DOS engine hacks
Tom Hall and John Carmack originally planned "The Universe is Toast" as the official commercial trilogy for Commander Keen. When id Software moved on to Wolfenstein 3D and Doom, that story arc lay dead for nearly two decades. Lead designer Ceilick set out to build the missing final chapter, starting development in 2009 after finishing Dead in the Desert.
Creating a true sequel required far more than swapping sprite graphics. Code patchers Levellass and Lemm broke apart the executable file for Commander Keen 5 to inject custom behaviors, revised sprite movement, and complex level transitions. Designers Mink and Tulip helped craft huge layout maps that stretched the old technology to its absolute limit. When the finished fan mod launched as freeware in 2011, it felt like an official commercial release from 1992.
Huge maps and pogo physics make every jump count
You begin on Mortimer McMire's hub space station after escaping planet Calidune in your Bean-with-Bacon Megarocket. Mortimer plans to detonate a giant star and incinerate the entire universe. To stop him, Keen must travel through teleporters to four separate planets, flipping control switches on each world to unlock the central door to the final Warpcore.
The standard platforming movement feels familiar right away. Keen can walk, jump, shoot his stunner raygun, and high-jump using his trusty pogo stick. Navigating areas like The Crater demands strict precision because the stage layouts are vast. A single missed pogo bounce over a pit of hazards usually means immediate death, forcing players to rely heavily on save states to survive the longer stages.
Every single level features its own original music track composed by Mr. M and ZidaneA. The soundtrack variety keeps the long platforming stages fresh, though not every song hits the mark. The track playing inside Altaire Station becomes grating fast, repeating a high-pitched loop that drives players to mute their speakers during tricky jumps.
The infamous Warpcore showdown and speedrunner tricks
The final gauntlet inside the Warpcore features a showdown against Mortimer McMire that test the patience of every veteran player. The boss encounter relies on tight target windows, unpredictable hazard drops, and zero room for error. One specific platform sequence in the chamber feels almost pure luck, forcing you to reload save states dozens of times before landing a clean hit.
Despite the steep difficulty curve, speedrunners discovered wild ways to bypass the campaign's structural barriers. The mod's engine scripting allows a trick known as "death-exiting." By dying directly on specific level triggers, players can exit a map while bypassing standard objective requirements. In total, 11 of the game's 12 major levels can be beaten optimized through this exploit, turning an intense trial into a rapid sprint.
Why Commander Keen 9: Battle of the Brains still demands your focus
If you enjoy classic action platformers, this project delivers level design that rivals id Software's commercial work. The original 16-bit DOS games were famous for crisp controls and secret passages, and this fan effort honors that tradition completely. The sheer scale of the maps and the clever sprite patches prove what creative modders can accomplish with classic DOS code.
The sheer difficulty of the late levels will frustrate casual players who expect a breezy platformer. The map sizes force careful exploration, and dying near the end without a save state hurts. Yet for anyone who mastered the original DOS trilogy, this mod gives you the truest conclusion to Billy Blaze's galaxy-saving adventures.
Jump into Commander Keen 9: Battle of the Brains right now
You can play Commander Keen 9: Battle of the Brains online free in your browser right here. There is nothing to install and no setup required to launch this fan-made Commander Keen 9: Battle of the Brains MS-DOS game directly in your window. Load it up, grab your pogo stick, and test your skills against the brutal hazards of Altaire Station today.