Man, this is tempting. I love me some rules-writing, and I adored Battletech back in the day, but I so do not have time for this. I wish I did.
*fondly recalls the oddest Battletech memory ever*
And friend and I had planned to spend our week-long 11th grade Thanksgiving vacation playing a huge Battletech scenario: a planetary invasion. We used, what was it, the Tactical Manual? Something like that? It had rules for fusion engines going critical, is all that matters.
Well, we each bought a regiment worth of mechs and vehicles and supplies, and we set up a few terrain locations using Geo-Hex (those wonderful styrafoam molded terrain pieces), and we planned to have a battle or two every day until one side won.
The first battle took place at a canyon that was sort of a moat defending the planet's capital city. Mechs from both sides descended into the canyon, and soon a close quarters brawl had ensued. Then I decided to focus fire on ... I think it was a Mad Cat. Pumped way too much damage into that mech in one round, and the engine went boom.
We eagerly flipped to the rules on engines exploding, and figured that with a 375 XL engine, it would do a ton of damage to all the mechs within 3 hexes. So we started assigning that damage, checking for critical hits as a few of the lighter mechs had their armor peeled away. Some ammo exploded, which dealt hundreds of damage to a medium mech.
Its engine subsequently exploded.
At this point we started laughing, as we realized that nearly every mech on the field was within 2 squares of another mech. We proceeded to spend an hour figuring out how far this chain reaction would go, as engine after engine went critical. Sure, a few mechs actually survived, but they had been half-slagged, and a lot of the ones that didn't explode were still crippled.
Of the twenty mechs that went into that battle, only 4 managed to walk out, leaving a nice radioactive crater in the middle of the canyon. We decided we could never top that, so the invaders just threw up their hands in frustration and left, and we played Goldeneye for the rest of the vacation.