Extracted from the 30 Mecha Design Flaws submission. Edited and reconfigured as a setting neutral piece for use in military aspected settings and most if not all flaws can be used on any vehicle or large piece of hardware.
The 228th Mountain Lion battalion faced a situation not entirely unlike General Custer some 500 years before. Like Custer's men, the 228th was almost completely destroyed, despite their laser cannons and drop ships.
All you need to stop a brain is a bullet.
30 generic problems to dole out for homebrew, custom made, and scratch built machines
The walking siege engines of the Cosmic Era
The Rocky Mountain Republic owes in large it's existence to a single limited run of primitive mechs, the Assault/Bombard Mech model 1.
Technology in the Cosmic Era can become corrupted and infested. When this happens to a mecha, the result in codenamed a Hekatonkheire.
The home base of the mighty mech
The reasons that mecha are not reliable as weapons of war are manifold, but the world changed more than many people expected and the way wars are fought have changed greatly since the middle of the Petroleum Era.
A common light mech of the Atlantic Federation
The ultra minimalism mech, for the common consumer
While technically alive, magnagogs have little in the way of personality and are driven via telepathic command.
The Sogans were a mystically aware technological society. Queen Stavarang is the last surviving Sogan in the galaxy
A desolate region is almost entirely without normal vegetation. Local plants are able to unroot themselves and crawl along the ground in search of water and fertile soil. The inhabitants fence their crops in to keep them from wandering off and put heavy stone thresholds in the doorways of their huts to keep wayward plants out.
The plants sense by chemical cues, lacking sight or hearing, and tend to avoid herbivores or anything that smells of "dead plants". Characters with horses are likely to be unwelcome among the locals.