CAIRNMECH

 

Hacking the Cairn RPG to run Battletech; my take on a way to put massive, stompy mecha into Oddlike TTRPG games.

Back in 2017, Chris McDowall (Into The Odd, Electric Bastionland, Mythic Bastionland, etc.) actually created rules for using mecha in Into The Odd (and by extension, Oddlike games, of which Cairn could be considered one.) It’s called Fighting Machines and it’s a good, simple plug in that you can use to emulate and run a satisfying mecha-centric game.

Unfortunately, as an avid Battletech player, it just didn’t fit quite right for me. I need that Oddlike Mechwarrior experience, my Electric Battletroops-land as it were. I want mechs, but I want them to be dead simple, satisfying, and terrifying for the party unfortunate enough to find themselves outside of a cockpit, facing one.

Between my work on running 28mmBattletech with Ivan Sorenson’s Five Parsecs From Home, my Battletech x BELLONA conversion, and the fact that I’ve read through a ton of the mecha-focused RPG systems out there, from the celebrated to the obscure (shout out to the amazing game Celestial Bodies, btw) I figure I’m in a good place to create something like this. As such, I present to you, CAIRNMECH, a bolt-on for Cairn (or rather, for Cairn-powered sci-fi “hacks” and games like MONOLITH or CY_CAIRN. If you use this, I’m not going to tell you what kind of Dire Wolf you can or cannot throw at your intrepid party of Kettlewrights, but if it’s the 100 ton kind carrying large lasers, well, that’ll be an interesting change of pace for your party of PCs for sure.

BASICS:

Mechs (and their cousins, battlearmor and protomechs) are towering steel machines studded with weaponry. They are stompy buildings with guns and pilots.

ARMOR AND GEAR:

Because of their size, Mechs are the only things that (with some rare exceptions) can have an ARMOR higher than 3 (but as a warden, YMMV.) The ARMOR of a mech is determined by its weight class (see below.) Weight class also determines the number of GEAR SLOTS a mech has and, for ease of use, these numbers are twice the value of the ARMOR.

ARMOR functions as normal. GEAR SLOTS represent the mech’s ability to carry weapons and state-of-the-art equipment that enhances its combat performance.

To give players (and beasts) a chance, whenever a damage die is rolled in an attack against something with an armor value equal to or higher than that damage die’s highest value (4 on a d4, etc.) it still does 1 point worth of damage. Blast rules still apply and take precedence. Yes, this does mean that you can technically stab a mech with a knife until it explodes. Good luck!

When determining DEX, use the pilot(s)’ value.

All mechs are assumed to move at a fast human running speed by default, though certain gear types can increase this speed.

WEAPONS:

Mechs may only make one attack per turn as normal by default, though certain gear types can increase the number of attacks.

A mech may make OVERHEAT ATTACKS to fire an additional weapon, but the mech will also take damage equal to half the damage dealt by that attack each time.

A mech may mount one or more of the same weapon. Gear that “stacks” may be added multiple times to a mech. Any other gear can only be applied once.

CRITICAL HITS:

If the mech takes damage to its STR, roll on the chart below to determine what kind of critical damage has been suffered:

GEAR TYPES

Each piece of gear below takes up ONE GEAR SLOT on a given mech. BULKY gear takes up two slots. This gear is not balanced, nor is it proofed against min/max configs. These are simply meant to be used as templates or conversion aids when converting a mech from Battletech to Cairn using this system. More information on this can be found in the DESIGN NOTES section below.

SMALL LASER: This mech gains an attack: d8 Blast. Ignores up to 2 points of armor.

MEDIUM LASER: This mech gains an attack: d10 Blast. Ignores up to 3 points of armor.

LARGE LASER: This mech gains an attack: d12 Blast. Ignores up to 4 points of armor.

PPC (Bulky): This mech gains an attack: d10 Blast. On a 9 or a 10, roll a critical hit on the target.

AUTOCANNON 2 (Bulky): This mech gains an attack: d4+d4 Blast.

AUTOCANNON 5 (Bulky): This mech gains an attack: d6+d6 Blast.

AUTOCANNON 10 (Bulky): This mech gains an attack: d10+d10 Blast.

AUTOCANNON 20 (Bulky): This mech gains an attack: d20+d20 Blast.

ROTARY AUTOCANNON UPGRADE: All autocannons on this mech (except LB-X) are capable of making an additional attack (still triggers overheat if not sufficiently heat-sinked.)

LB-X AUTOCANNON 2 (Bulky): This mech gains an attack: d4 x2

LB-X AUTOCANNON 5 (Bulky): This mech gains an attack: d6 x2

LB-X AUTOCANNON 10 (Bulky): This mech gains an attack: d6 x4

LB-X AUTOCANNON 20 (Bulky): This mech gains an attack: d6 x8

LONG RANGE MISSILES (LRM) 5: This mech gains an attack: d6 Blast

LONG RANGE MISSILES (LRM) 10: This mech gains an attack: d10 Blast

LONG RANGE MISSILES (LRM) 15: This mech gains an attack: d12 Blast

LONG RANGE MISSILES (LRM) 20: This mech gains an attack: d20 Blast

SHORT RANGE MISSILES (SRM) 2: This mech gains an attack: d6 Blast

SHORT RANGE MISSILES (SRM) 4: This mech gains an attack: d12 Blast

SHORT RANGE MISSILES (SRM) 6: This mech gains an attack: d20 Blast

GAUSS RIFLE (Bulky): This mech gains an attack: d10+d10 Blast. Ignores up to 4 points of armor.

AP GAUSS: This mech gains an attack: d12 or d4 Blast.

MACHINE GUN: This mech gains an attack: d12 or d4 Blast.

ANTI-MISSILE SYSTEM (AMS): passively prevents up to d12 damage from missile weapons in a cycle.

FLAMER: This mech gains an attack: d12 or d4 Blast or mech target may make one less attack next turn without overheating.

HATCHET / SWORD / MACE / ETC.: Damage dealt is dependent on weight class. BA, Proto and Light = d6+d6 Blast. Medium = d8+d8 Blast. Heavy = d10+d10 Blast. Assault = d12+d12 Blast. Superheavy = d20+d20 Blast.

HEAT SINK ARRAY: This mech may fire an additional weapon each turn (stacks)

LARGER ENGINE: This mech moves twice as fast (stacks)

SUPERCHARGER: In place of an attack, casts the Haste spell on this mech for this cycle and the next one..

TRIPLE STRENGTH MYOMER: This mech gains +2 STR (Max 20) Not compatible with M.A.S.C.

M.A.S.C.: Whenever this mech takes damage from an overheat attack, it gains the effect of the Haste spell next turn.

JUMP JETS: This mech can lift off and fly limited distances.

COMMAND CONSOLE: This mech has a second cockpit. When making WIL or DEX checks in this mech, both pilots roll and the best result is chosen.

TARGETING COMPUTER: All attacks by this mech ignore an additional 2 points of Armor.

C3 COMPUTER: This mech gains +2 WIL (Max 20)

FERRO-FIBROUS PLATE: +4 HP.

ENDO-STEEL STRUCTURE: +2 DEX (Max 20)

DESIGN NOTES:

This all started with thinking about dragons, or rather, with thinking about how they are represented in Cairn. Dragons are a big deal in Cairn. You don’t just march in as a footsoldier and go toe to toe with one, and that’s how I see Battletech mechs. In Oddlike RPG system play, I want mechs to feel titanic and unbeatable, but I also want them to have statistics so they can fight each other or be taken down with a well-planned ambush.

While you won’t end up with a straight-across conversion of Battletech to Cairn here, my goal is to bring out the flavor of infantry scale Battletech within an oddlike system, I especially wanted to bring out the flavor you see in the Battletech fiction books, where an ambush with inferno SRM infantry units can take down a Locust before it can bring those machineguns to bear on a city.

Speaking of, these might give your characters an edge:

INFERNO SRM LAUNCHER: (Bulky) d8 blast or mech target may make one less attack next turn without overheating. Sets things on fire with space napalm and they keep burning. Each reload takes up one additional inventory slot.

VIBROMINE: (Bulky) Seismically activated mine that can be set to go off whenever a mech target of a certain weight class is nearby. Mech target must Save DEX or take d6+d6 STR damage (bypasses armor.)

MAN-PACK PPC: (Bulky) d8 Blast. On a 9 or a 10, roll a critical hit on the mech target. Needs to cool down between shots.

Alternatively, if you want a straight across conversion, you can always do mech battles using Battletech / Alpha Strike and use Cairn (or Monolith, etc.) In place of one of the official Mechwarrior RPG systems (which are too crunchy for me, personally.) There’s nothing wrong with bouncing between game systems whenever a pilot climbs in or out of their mech. In fact, the fragile nature of characters in Cairn meshes well with the fragile nature of pilots in Classic Battletech, so playing out-of-cockpit scenes with Cairn and mech battles with Battletech could work really well.

EXAMPLE UNITS:

ELEMENTAL BATTLE ARMOR: HP 8, Armor 3, STR 14, Small Laser, SRM 2, Machinegun, Jump Jets, Heat Sink Array x2

SIREN PROTOMECH: HP 12, Armor 4, STR 15, Machinegun x2, Larger Engine x5, Heat Sink Array

ROC PROTOMECH: HP 12, Armor 4, STR 15, Medium Laser, Larger Engine x5, Jump Jets, Heat Sink Array

MINOTAUR PROTOMECH: HP 12, Armor 4, STR 15, Medium Laser x2, Larger Engine x4, Jump Jets, Heat Sink Array

LOCUST LCT-1V: HP 16, Armor 5, STR 16, Detachment, Medium Laser, Machinegun x2, Larger Engine x5, Heat Sink Array x2

URBANMECH UM-R60: HP 16, Armor 5, STR 16, Detachment, Autocannon 10, Small Laser, Heat Sink Array x6, Jump Jets

FIRESTARTER FS9-H: HP 16, Armor 5, STR 16, Detachment, Medium Laser, Machinegun, Flamer x2, Larger Engine x2, Jump Jets, Heat Sink Array x3

PNT-9R PANTHER: HP 16, Armor 5, STR 16, Detachment, PPC, SRM 4, Larger Engine x2, Jump Jets, Heat Sink Array x5

HUNCHBACK HBK-4G: HP 20, Armor 6, STR 17, Detachment, Autocannon 20, Medium Laser, Small Laser, Larger Engine x2, Heat Sink Array x6

SHADOWHAWK SHD-2H: HP 20, Armor 6, STR 17, Detachment, Autocannon 5, LRM 5, SRM 2, Medium Laser, Larger Engine x2, Heat Sink Array x5

NOVA / BLACKHAWK: HP 20, 6 Armor, 17 STR, Detachment, Medium Laser x5, Heat Sink Array x4. Larger Engine x2, Jump jets

RIFLEMAN RFL-3N: HP 24, Armor 7, STR 18, Detachment, Large Laser x2, Medium Laser x2 Autocannon 5 x2, Larger Engine x2, Heat Sink Array x4

TIMBERWOLF / MAD CAT: HP 24 (28), Armor 7, 18 STR, Detachment, Ferro Fibrous, Endo Steel, Larger Engine x2, LRM 20 x2, Medium Laser x2, Heat Sink Array x4

CHARGER CGR-1A1: HP: 28, Armor 8, STR 19, Detachment, Small Laser x5, Larger Engine x4, Heat Sink Array x7

ATLAS AS7-D: HP 28, Armor 8, STR 19, Detachment, Autocannon 20, LRM 20, SRM 6, Medium Lasers x4, Larger Engine, Heat Sink Array x7

DIRE WOLF / DAISHI: HP 28, Armor 8, STR 19, Detachment, Large Laser x2, Medium Laser x2, Autocannon 2 x2, Rotary Autocannon Upgrade, LRM 10, Heat Sink Array x6