Codenamed Puma by Inner Sphere forces who first engaged it, the Adder is a light Clan OmniMech that serves as a direct or an indirect fire-support unit in most of its configurations. The Adder is capable of carrying a relatively heavy weapons payload that can surprise an unsuspecting enemy, even at extreme ranges.
The Adder was designed by Clan Star Adder in preparation for the invasion of the Inner Sphere. First produced in 3010, the formidable Adder was actually designed as an OmniMech capable of emulating the weapons configurations the Wolf's Dragoonsreported as most common for medium Inner Sphere BattleMechs, the 'Mechs most frequently fielded by Successor State armies. Some of these configurations, including B, C, and D, are still used as of 3050. Despite producing such a formidable design, the Star Adders failed to maintain exclusive possession of the Adder; by 3045, the Adder had become common throughout the Clans.
The Adder frees up as much weight as possible by using a weight-saving Endo Steel chassis and carrying a lightweight 210 XL Engine, which gives the 'Mech a top speed of 97.2 km/h. The Adder carries six tons of Ferro-Fibrous armor for protection from enemy fire. The effort to save weight has resulted in a 'Mech that dedicates almost half of its weight to pod space. [Source: sarna]
You can download the papercraft model here: MechWarrior 4 - Adder (Puma) Free Mech Paper Model Download