In the Madness series, obstacles usually take the form of shipping containers such as boxes, crates and barrels as well as other miscellaneous items like flipped-over tables and silos. They have been seen in the background throughout the Madness Combat episodes. They usually serve as mere background items, but are sometimes used to take cover from bullets and other various uses, such as a weapon by Jesus in Madness Combat 8. Obstacles have appeared in nearly every animation since Madness Combat 3: Avenger.
Madness: Project Nexus
Obstacles are most importantly seen in Madness: Project Nexus (Classic). The player may use them as cover to reduce damage. In Arena Combat Mode, two metal barrels are used as obstacles. If one is damaged enough, it'll start to break and the user will have a higher chance of getting hit behind cover.
In Zombie Arena Mode and Episode 1.5, crates are included for cover instead of the usual barrels. The-Swain stated that there would have been more cover options in Episode 2 of Project Nexus.