Gamemaster's House Rules
Salvage, Repair, and Rearm:
General Salvage: Salvage is handled as observed in the computer game MechWarrior 3. No rolls are necessary with one notable exception (see: The Donut Rule). As long as a component has not had all of its criticals destroyed, the component can be recovered and repaired (see "General Repair," below, for exceptions). A 'Mech can be recovered if it has lost one or both legs. The GM has discretion on if an enemy 'Mech is a total loss or not based on the level of internal damage a 'Mech has sustained; player 'Mechs may be restored from the edge of destruction and are also subject to the Donut Rule.
The Donut Rule: A 'Mech that has lost only the Center Torso (it may lose the head) could still be recovered, with all equipment in the Center Torso intact. On a 2D6 die roll of 8 or better, the unit is recovered. On a 7 or less, it is not recovered and it is stripped for parts instead.
General Repair: Individual armor points that are not Standard Armor are tracked, as are internals that are not Standard Internals. Actuators, hatchets and other melee weapons, communications equipment, single heat sinks and all cockpit components are also untracked. Double Heat Sinks, Jump Jets, and all weapons and ammunition are tracked. As long as one critical slot remains undamaged on a part (such as a large laser that took one hit, for example), the component can be repaired, and does not need to be replaced. The GM facilitates all repairs and requires no intervention from the players, unless a destroyed component lacks a replacement or the force has run out of armor or ammo.
Engines and Gyros: A standard engine that has taken 4+ hits, a standard gyro that has taken 3+ hits, a Heavy Duty or XL Gyro that has taken 4 hits, or an (X)XL Engine that has taken 6+ hits is considered ruined and must be replaced. Compact Engines that take 3 hits are ruined, as are Compact Gyros that take 2 hits. Vehicles with fusion engines that have taken an engine hit will need a replacement engine. ICE Engines can be "ruined" but are considered an untracked item because of the relative ease of replacement and procurement.
Clan Parts and LosTech: An ammunition explosion within a location containing CASE will typically destroy the location. The CASE that prevented the total annihilation of the unit may still be recovered on a roll of 6+, even if the 'Mech was later destroyed. (If the force has 20+ units of CASE, this roll will not be made.) In all other cases, strictly to make the GM's job easier, all damaged LosTech equipment falls under the same repair rules as readily available equipment, even if the knowledge to do so was otherwise perceived lost. Clan weapons and equipment fall under the same rules for the exact same reason. Clan CASE is integral to the structure of the Clan unit and is neither tracked nor rolled for, however it cannot be mounted on Inner Sphere units.
Repair Time: Repairs take 8 hours regardless of damage done, but on a rare instance where missions are back to back in-game, a patch of commercial armor will be bolted onto any location that a 'Mech has less than 5 armor, up to 5 armor or the limit set by the configuration, whichever is lower. Patch armor is free. If the force has run out of spare armor, the patch armor rule from here is used.
General Rules: MechWarriors may customize almost any aspect of a BattleMech except for the engine, gyro, cockpit, and internal structure (exception: see "Factory World"). Customizations take a period of time depending on the number of changes that are done. There is no chart for this as it is arbitrary and generally up to the GM. Generally, smaller changes will take about a week in-game, with more substantial changes taking up to one month of in-game time. A MechWarrior may change the armor type of a 'Mech, even to Clan Ferro-Fibrous on an Inner Sphere 'Mech.
Factory World: Once contact is made with a major manufacturer when on a world with one, a 'Mech's engine, gyro, cockpit, and/or internal structure can be changed, as long as the force has the parts to go through with the changes. In most cases, these changes will cost C-Bills.
Weapon Limit: MechWarriors are encouraged to keep to the basic spirit of a 'Mech when customizing it, but are not restricted to do so. A 'Mech's combat computer can typically handle only so many weapons on the 'Mech. The limits are below, and take the highest limit:
1: The tonnage of the 'Mech divided by 10, rounded up
2: The number of weapons that the base, standard configuration of a 'Mech has, plus two
3: The number of weapons that an official variant configuration has (up to the campaign's year), or
4: Five weapons
If the 'Mech is an OmniMech, the weapon limit is 16.
OmniMechs: OmniMechs are customized at the same time frame that repairs are done, which is within eight hours in-game. Weapon Pods are not tracked, and will be compatible with both Inner Sphere and Clan technologies. Unlike standard 'Mechs, an OmniMech's armor and armor type cannot be customized, and anything that is fixed must stay fixed. Engines and internal structure cannot be modified on an OmniMech, even with access to a world's factory.
Clan Technology: Clan components will work on Inner Sphere units and vise versa. Ammunition with Clan Weapons: Due to the way that Clan LRM launchers and Clan Streak SRM launchers work, their ammunition types (as well as AMS) will be differentiated from Inner Sphere ammo. All other ammo types not listed should be compatible with their Inner Sphere counterparts with minimal effort.
Individual Initiative: Enabled on MegaMek, Individual Initiative means that each unit on the field must roll for initiative instead of each team. This reinforces the RPG-lite nature of these games that much more, and allow for an additional Initiative quirk, below. To speed the game along, Weapon and Physical attacks are all declared simultaneously, but not Movement.
Weight Class-based Initiative: Inspired by the upcoming BATTLETECH computer game's turn order, units of lighter weight classes will have an initiative bonus. Assault units have a bonus of 0, while Heavies get +2, Mediums get +4, and Lights get +6. Vehicles get a -1 on top of their weight class bonus due to their more clumsy nature. MechWarriors may increase their individual initiative beyond these bonuses through spending EXP.
Weapons Specialization: A MechWarrior that chooses to specialize in one weapon (a 30 EXP purchase, see Roster -> Earning/Spending XP) will get to specialize in closely related weapons as well (such as a Large Laser, ER Large Laser, and Large Pulse Laser all being in the same group, but a Small Pulse Laser or a Medium Laser will be different). Due to MegaMek limitations, they must choose one or the other if multiple types of that weapon are mounted.
Tactical Operations and Unofficial Rules in Play:
Skin of the Teeth: Life is hard enough on a MechWarrior, and when a player is attached to one, it's especially heartbreaking when they lose him or her. A 'Mech that has lost the Head location has one last chance to eject. After making a successful piloting skill roll, they have escaped death, but only barely. Purchasing the skill Pain Resistance greatly increases the odds of the MechWarrior surviving a terrible fate.
Sprinting, Evasion: Sprinting allows a 'Mech to enter or exit the action quicker, with some penalties such as not being able to shoot. Evasion allows a 'Mech to dodge out of harm's way a little better while on the move, but cannot fire.
Fire!: Enemies and players alike may set fire to woods, fields or buildings to create smokescreens or to create a major inconvenience for hot units. Woods will slowly burn and take Terrain Factor damage per turn. I'd hate to be the guy that has to use those rules in actual tabletop play, though, thank goodness for MegaMek!
Piloting Skill Rolls: Weight-based PSRs during stagger checks apply, as does increasing amounts of damage affecting the odds of succeeding on a PSR. The heavier the 'Mech, the harder it is to topple. In addition, lighter 'Mechs making physical attacks get a bonus to strike their opponent.
A piloting skill roll is also made if a unit wants to change levels backwards. A failure drops the unit onto the lower of the two hexes.
Careful Stand: A 'Mech may spend its entire turn to stand at a -2 PSR bonus. This doesn't apply to 'Mechs that have 2 MP or less remaining due to damage or heat.
Hull Down: 'Mechs and vehicles may go Hull Down for additional cover. The vehicle must be next to a level higher to go hull down.
Firing While Down: Prone 'Mechs with one arm may fire at a higher penalty. The normal rule is that a 'Mech that is prone must have two arms to prop itself up to fire.
Line Of Sight: Units must draw line-of-sight using a relatively accurate diagrammed model.
Extreme Range: Weapons can now reach out to double their medium range at a new range bracket called "Extreme Range". Weapon damage is lessened slightly and the difficulty to hit at this range is +6 (or +3 for anyone with Sniper).
Ammunition Explosions: Being nearby an exploding unit is a bad state of affairs. If one unit is close to another that is exploding, they take 5% of the force of the ammunition explosion. (A ton of machine gun ammo will explode for 400 damage and do 20 damage to all nearby units, clustered like LRM Damage).
(Unofficial) If a unit suffers an ammunition explosion, but it is protected by CASE, the MechWarrior will only take 1 point of damage and rolls for consciousness like normal.
Gauss Rifles: Gauss Rifles may be powered down at will to avoid catastrophic damage when critically hit.
PPCs: Standard Particle Projector Cannons have a field inhibitor that prevent the cannon from exploding in a 'Mechs face when it is fired at point blank range. This can be disabled to remove the minimum range penalties of the weapon, at great risk of making the weapon explode. The weapon exploding is treated as an ammunition explosion and will injure the MechWarrior.
Ultra Autocannons: Ultra ACs normally roll on the "2" column of the Cluster Hits table if they hit their target. Instead, they now roll both shots as separate weapons. Because this introduced a weird quirk where the weapon has a chance to jam on either rolls, the Unofficial rule that Ultra ACs can be unjammed like Rotary ACs has been enabled.
Vehicles: Vehicles that have suffered an engine hit or have had their motive system trashed do not count as Immobile for determining the target to-hit. This primarily allows vehicles to last that little bit longer as glorified bunkers. In addition, to add a human element, vehicle crews may abandon their vehicle if they feel like they are in sufficient danger of dying. (The destruction of any vehicle's location will kill the crew.)
(Unofficial) Vehicles are also a little less likely to suffer critical hits to offset their delicate nature.
Expanded Heat Scale: The heat scale now has additional effects beyond 30, which can include more severe penalities like system failures, pilot damage, and guaranteed ammunition explosions. Using the expanded heat scale makes it easier to override shutdowns at lower levels based on the MechWarrior's base Piloting skill.
Loose MechWarriors: Ejected MechWarriors and vehicle crews will no longer be at the mercy of the battlefield, but at the mercy of the victor's salvage crews instead. While probably unsatisfying that a player cannot kill an NPC MechWarrior that has fled their 'Mech, this is primarily to speed the game along.