Crab CRB-20 is a Medium-class 'Mech in Battletech.
Crab 20s fulfill an oft overlooked role, that of a skirmisher with firepower. Wielding strong energy weapons, the Crab delivers a punch at nearly all ranges, with no ammunition constraints. The blend of firepower, heat efficiency, and speed make the Crab the perfect 'Mech to raid enemy positions.
The list of viable crab builds is a fairly short one owing to the 'mech's limited hardpoints. There are only seven to work with, five energy and two support, and they are distributed in an unfavorable layout. You're only ever going to have six weapons at best, as the two head hardpoints cannot be used simultaneously and, once cockpit mods come into play, likely won't be used at all. This leaves three hardpoints in the torso, which isn't high on slots either, and two in the arms, which are likely to do the bulk of the work here.
- Optimized Stock Loadout - The lone Small Laser contributes little to the Crab's Fire-Support/Skirmisher role, and can be cut for extra armor, or a Jump Jet.
- Medium Lasers - Medium lasers are the mainstay weapons of lighter 'mechs across Battletech, and an array of five of them can carve open early and mid-game opponents quite handily, though it'll rack up heat fast in the process. Employing hit-and-run tactics (likely with JJs) can make this quite viable.
- Long Range Fire Support - Large lasers can allow the crab to plink away from safer ranges, relying more on distance than heat-generating JJs to keep itself alive through the encounter. Two LLs with some heatsinks can maintain consistent fire even on fairly hot maps, though it's going to take a while to carve through anything substantial on the field. Three LLs won't be alpha striking every turn but do provide more punch when needed. Note that large lasers can be somewhat difficult to come by during the parts of the game where the Crab is most viable, if you're playing the campaign.
- LL + ML combinations are likely to run hot as they combine the high heat generation of the MLs with the high tonnage of the LLs, leaving little room for heat sinks, but they can be quite punchy up close while still retaining some ability to hit from farther out if forced to draw back from the front lines.
- The support hardpoints are too few in number to base a build on, but if you have some tonnage to spare, a small laser can readily add some extra firepower for very close engagements. Again, hit-and-run is recommended here.
- PPC Scout/Sniper - With some sacrifice of armor, PPCs can be viable weaponry for the crab if you don't expect to be firing them every turn. This can be very effective when the Crab is used as the scout 'mech on a lance with lots of stability damage, as it can alternate between sensor locking a target on one round to allow its friends to rain missiles on it, then starting the following round by using the PPCs to give the enemy 'mech the final push to send it toppling over. Be ready for heat problems galore, though, especially if your crab enjoys frequent flyer status.
- The Crab's most comfortable role is quite effectively spelled out in its in-game descriptions: a hard-hitting skirmisher that doesn't need to worry about ammo.
- Now patched, the Crab runs faster than other 'mechs in its weight class (the Centurion, Hunchback, and Enforcer), and while it doesn't quite bring as much firepower to the fight as they do, it can mount an extra jump jet and so render itself a much more slippery foe. This makes hit-and-run tactics viable as both a way to keep the Crab safe and reduce heat problems pre-Ace Pilot.
- The crab's speed is sufficient to generate a solid quantity of evasion chevrons, which as a medium 'mech it should be doing every turn.
- As the game progresses, the Crab can transition capably from skirmisher to flanker and scout roles. It's not all that much slower than a Firestarter, which would likely fill said roles otherwise, and it is a lot more durable. With the right build, it won't need to get close to the enemy to hurt them either.