Black Knight BL-6-KNT is a Heavy-class 'Mech in Battletech.
With a PPC, two Large Lasers, and four Medium Lasers, the Black Knight has devastating firepower - and equally devastating heat buildup. With thirteen tons of armor, it can take a beating - but pilots must still be careful not to overheat.
Dump the Large Lasers in favor of a second PPC and three more heat sinks. If you really want to be adventurous, dump two of the ML's in favor of Flamers, but this mech is slow enough that it is doubtful you'll be able to use them very often, so another pair of heat sinks might be a better trade.
Alternatively, for a close range brawler, you can turn it into a 'Super-Grasshopper', by replacing both the Large Lasers and PPC with additional Mediums, Armor, and Jump Jets. In the campaign, it serves as a very capable point man for the early midgame, soaking up for you actual damage dealers, at least until you can secure your first Battlemaster.
The Black Knight has the most available tonnage of any non-Lostech Heavy-class mech (along with the Orions) currently in the game. This means that while the Grasshopper also has 7 Energy Hardpoints, the Black Knight can devote more tonnage to additional heatsinks or heavier weapons. When running both mechs, a good option would be to configure the Grasshopper for short range firepower, and the Black Knight for Medium-to-Long range firepower.
Snub PPCs. Just. Snub PPCs. One on each arm, four medium lasers, and enough armour to knife-fight a King Crab, with a couple of Jump Jets and an Exchanger. A set of MGs would also be adviseable if you intend to use it in close quarters, preferably the ++ versions which have no weight and a +50% crit chance, with one ammo bin. At least ten heatsinks if you intend to use it anywhere other than polar environments.
The BL-6-KNT has 24.63 tons available after full armor or 42.5 tons with no armor. This is the same as the Marauder MAD-3R and Orion ON1-K. The Grasshopper GHR-5H has 24.19 tons available after full armor or 41 tons with no armor.
The Black Knight 6-KNT is a dedicated Energy weapon platform. It can shell out hellish damage with its beams and shrug off a lot of damage, just gotta make sure to keep its heat in check.
For a mech pushing up on Assault tonnage, it's surprisingly fast. Get in close and engage with the excellent melee capability, especially if you can find a few tons for support weaponry and arm mods. If you're looking for a brawler in the Heavy class, look no further, especially if you can find some ice or water to fight on. Since the melee is so good, running hot isn't so much of a problem for this mech - so long as your loadout can fire two salvos without overheating, you should be able to get into melee and cool down by the third turn. Use it as you would a Battlemaster or Awesome who traded ten tons for a higher initiative.