Assault-class BattleMechs range from a mass of 80 tons to the maximum of 100 tons, and are generally regarded as the centerpiece of forces large enough to support them. From the humble Victor to the incredible Atlas, Assault 'Mechs are defined by their ability to define the battlefield. An Assault 'Mech present on the battlefield usually changes things, forcing strategies to deal with them or be dealt with in turn. They are often quite rare outside of armed forces, and the logistics of sustaining use of one can often be outside the range of smaller mercenary outfits.
80 Tons
Awesome
Known models: AWS-8Q
When considering the Awesome, one finds an Assault-class BattleMech designed for exactly one use, and given all the tools to do it exceptionally well. It is armed with three PPCs, and enough heat dissipation to fire them almost non-stop. On top of this, it is well-armored with good coverage, making it an exceptionally effective direct-fire support BattleMech.
Victor
Known models: VTR-9B
Designed as a support BattleMech with jump capabilities, the Victor was quite good at support by being able to jump into a close-range fight and bring its heavy firepower to bear. Its primary weapon in the right arm is a Class Twenty Autocannon, backed by two Medium Lasers and a four-missile Short-Range launcher. With these weapons it is able to bring a notable amount of damage into the fray with little warning in rough terrain.
Zeus
Known models: ZEU-6S, ZEU-6T
A signature Lyran Commonwealth Assault BattleMech, the Zeus is something they stand by with pride. It is armed with a Class Five Autocannon, a Large Laser, and a fifteen-missile Long-Range launcher. With this armament, it is designed to engage at range and use a faster speed than most Assault-class 'Mechs to keep up. The ZEU-6T model exchanges the autocannon for a PPC and extra heat sinks, making it very dangerous when allowed to engage at moderate ranges.
85 Tons
BattleMaster
Known models: BLR-1G
The BattleMaster holds a distinct place as a centerpiece in a great many lances, being versatile and well-protected. Its primary weapon is a PPC, allowing it to fire at decent ranges, but closing with it allows it to introduce the short-range firepower it has. This includes four Medium Lasers and a six-missile Short-Range launcher, enough to deter most 'Mechs from trying to step up toe-to-toe with it.
Longbow
Known models: LGB-0W, LGB-7Q
An Assault-class missile fire-support 'Mech, the Longbow is very much similar to the Catapult in general design using weapon pods for arms. Its main armament is concentrated in two twenty-missile Long-Range launchers in arm pods, backed by two smaller five-missile Long-Range launchers in the torso. A considerable amount of ammunition and speed for its weight allow it to be a formidable fire-support platform. The 7Q model is designed to be slower, but with much more armor to allow it some stamina in a longer battle.
Stalker
Known models: STK-3F
A design not unlike a steel blimp with weapon pods on the sides, the Stalker is eighty-five tons of armored menace. Each side weapon pod contains two Medium Lasers and ten-missile Long-Range launchers, while the side torsos accommodate a Large Laser and six-missile Short-Range launcher in each. It is meant to steadily and methodically dismantle any single target, and with all these weapons it can very much do that.
90 Tons
Cyclops
Known models: CP-10-Z, CP-10-Q
The "single eye" of the Cyclops is a distinctive part of the BattleMech, and it is an older style of command BattleMech. It is armed primarily with a Class 20 Autocannon, and a ten-missile Long-Range launcher. For short-range firepower in addition it has a four-missile Short-Range launcher and two Medium Lasers. The CP-10-Q model instead is armed with a second Long-Range launcher and another Medium Laser, on top of having a good deal more armor added to its frame. To find a Cyclops with all working equipment for the command systems is rare, but they remain placed in the role all the same.
Highlander
Known models: HGN-733
A Highlander is designed as a defensive unit, for urban or base defense. With jumpjets, it can handle such terrain, and its armaments help it use that for leverage. It is armed with a Class Ten Autocannon and twenty-missile Long-Range launcher, backed by two Medium Lasers and a six-missile Short-Range launcher. A relatively rare sight, the Highlander is more infamous for the "Highlander Burial", which describes a Highlander jumping and planting both feet into a lighter BattleMech to do crippling damage.
95 Tons
Banshee
Known models: BNC-3E, BNC-3M
When it was designed, the Banshee was intended to be a fast close-quarters BattleMech, but the desired speed meant a great deal of its mass is devoted to the engine. The armaments of the Banshee's base model thus is rather light, in the form of a Class Five Autocannon and a PPC, but the speed and armor of the Banshee often is enough to make it worthwhile. The BNC-3M version, on the other hand, has two Medium Lasers and two PPCs, being able to put the speed and armor to use acting as a deterrent for getting too close to support units.
100 Tons
Atlas
Known models: AS7-D
If the BattleMech is the king of the battlefield, then the Atlas is the king of kings. Heavily armored, heavily armed, this design uses every bit of the hundred tons it masses in order to give it the edges which might be needed. Its primary armaments are a Class 20 Autocannon, and a twenty-missile Long-Range launcher both in the torso. Backing this up are a Medium Laser in each forearm, and a six-missile Short-Range launcher to give it a considerable short-range damage potential. It is a juggernaut in every sense of the word, incredibly difficult to stop without fully destroying it. Or being remarkably fortunate.
When you see an Atlas, run. When an Atlas is in your face, you ded, son.
Once I had a friend DM an impromptu RPG-Battletech hyprid session where he equipped an Atlas with turbo speed and a giant sword. We all died. Horribly.