Both of the Extra Areas in the game are antimaim-type upgrades, but there was always a third type of Extra Area that I kept trying to include in the game but never quite got it right: The "Armor Purge" ability. Purgeable armor parts are a common genre convention, but they don't make a lot of sense as abilities in a point buy system. You can already buy any upgrades and weapons with MP, so locking your cool stuff under your other cool stuff doesn't make a lot of sense. Similarly, AI-controlled powerups and ejectable equipment need some tweaking in order to work in a system like BCG. The latter two concepts got into the game as the Extra Areas, whereas Armor Purge always suffered from fun or balance issues, never making it to the game.
Expansion Pack protects a whooping 30 MP of stuff from Maim status. It does this without costing Energy and comes with a free use of I Cannot be Defeated attached as a bonus. It is kind of really, really powerful. Oh sure, you'll lose all the stuff installed there when you purge it, fair enough. You know what else disables your Upgrades and Weapons? Exploding, which is what would happen to your Mecha without the purge effect. You could build with a Plan B in mind, to let you continue fighting effectively after a purge - or you could just not bother, because it is a really good deal as it is. Expansion Pack only costs 5 more MP than an Assistant granting the aforementioned Genre Power, and only 5 more MP than Integrated Weapons... But it protects your Upgrades and not just your Weapons. Would it surprise you to know that it was nerfed like 3-4 times and this was the weakest version of them all?
Expansion Pack is an absurd upgrade and the only thing keeping it somewhat balanced is that it'll cost you almost two full power levels to fill it up with stuff, and by then you may want to buy some more External Upgrades and Weapons, only you don't have a way to keep them from getting disabled. Honestly, if deadlines didn't exist this probably would have been weaker. I'll give this an A on concept, because it represents a mecha trope faithfully and feels good to play with, but it gets a B on execution because the numbers it works with make it waaaaay stronger than intended.
This one is also very powerful, but less so than Expansion Pack. The idea is that your giant robot "awakens" after the fighting has been going for a while and that unlocks its most powerful Weapons and Upgrades. What balances this one is that battles are usually too chaotic for you to reliably control how long they will last. Sure, you can try to durdle and Maneuver for a few turns while Tension goes up, but that won't stop the pure damage from Extreme Terrain or Bombardment, and by the time you're done powering up it may be too late - it's just you vs all the enemies left while your team curses your ancestors and descendants both.
Secret Equipment could be free unmaimable MP (or a total waste of it) depending on your team composition and how willing the GM is to let you activate it in peace, so it is a gamble. BCG Operations tend to end quick when optimized PCs and NPCs are going at it, making this Upgrade very bad under those circumstances. That's why BCZ has Limit Engine to help you reach Tension 5 semi-reliably. The tradeoff is, of course, that you have to build around that and try to get the attention of enemy forces. Suddenly, you're not anymore a loner on cleanup duty, but a team player that tanks for the rest. I really like how that worked out.
If BCG wasn't a generic mecha system trying to adapt as many genre conventions as possible, I might have taken the easy way out and just skipped on doing these. Between the concepts being difficult to adapt and antimaims in general being difficult to balance, Extra Areas were pretty tough to work on. Fortunately, these two worked out and made it to print.
But they wouldn't be the hardest genre conventions to turn into Upgrades. Oh no, we've only just gotten started on headache-inducing content.
Next: Alternate Forms.