I'd like a game based around Pokemon's Underground from Gen 4 fleshed out to be more than just a feature.
Imagine a three-tiered gameplay setup. Stage one is a prep stage, player interaction is limited to small amounts of sabotage and petty theft, as everyone gathers riches and materials while researching tricks, traps, and trials for the enemy to go through. You'll immediately begin hoarding treasures and plotting the demise of your enemy, all while gaining bonuses for it- every item of treasure you dig up has two effects. The first is the effect it has when it's in your armory, generally a very small or weak upgrade to your base, depending on item (those you can't equip have better boosts) and a different effect when equipped on your person. A ring might add 1% trap activation speed for your base, and would give you +5% chance to not activate traps. The downside? Dying on enemy territory drops all your equipped items on their field.
Once all the resources have been collected in the time frame allotted, you build your horde to drive enemies out and keep the loot coming. Monster spawners, hidden doors, spike traps, slippery floors, Rube Goldberg components, high explosives, fake treasure rooms, puzzle doors, tripwire alarms, Indiana Jones boulder traps... And that's just the design elements.
Finally, there's the Combat round. Combat still allows you to build, change, re-arm, and upgrade traps, however you must now be inside your horde and you'll be vulnerable doing it. Now's the time you need to go thieving!
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A similar working is Station, an idea based around Space Station 13 meets The Purge meets Gundam.
Players take turns designing stations and attack fleets. Stations have control of where the entrances are (there are limits, as they can only be so close to each other and cannot directly connect to the same hall) and where their Bridge is, the enemy target. They must place workplaces strategically, and choose defense mechanisms to stop the enemy advance. Player characters can choose their role similar to SS13, but so can enemies now. For instance:
The Station Crew has built a station where the three entrances all connect to hallways near the front of the vessel that connect early but stay branched, with maintenance shafts between the halls and off to the sides of the ship. Security is close to the bridge and Medical, Science on the opposite side of Medical, and then more civilian and service jobs off closer to entry points.
The enemy has decided to warp-drive in close by and launch each member in a combat hardsuit. This takes a good number of points and each member is not well armed outside of their suit, only able to take a favored weapon and ballistics or antishock armor. This leads to a late alarm being raised as the attack is very sudden, and defense mechanisms lock onto the ship rather than the hardsuits. One is lost when closing into the entrance, but the attackers are very successful in landing. The hardsuits immediately scramble, anything with range taking the main hallways as other hardsuits take the maintenance tunnels. Internal lockout systems start to come online, but as they had no time to prime, are either torn through or simply too late. Knowing this, all available assets have been stockpiled around Security, the scientists and medics preparing some scientific weapons (special grenades being the most common as well as upgrades to weapons) for the security crew. Able to build a couple of weak EMP grenades, they prepare for their last stand.
And the hardsuits rip through the last blast door. Meeting them are two EMP proximity mines, immediately disabling most of the forward force and forcing the survivors to take a new route. Those who didn't die by sudden electrocution were taken out by the security crew, and there's a brief silence.
Suddenly, the maintenance doors explode outward as the secondary force backed up by the couple of surviving suits pincer the security force. Their fortifications are destroyed but the suits are rendered inoperable due to damage. Both sides have few people and supplies left.
The last assault on the bridge begins. Using an immobile but functioning suit, the attackers blast a hole in the side of the Bridge. Ballistic fire cuts down one operative as the others scramble for cover.
The attackers send out someone with ballistic armor, to use some of the near-depleted laser rifles to soften up the enemy guard as the others move closer. Hopping from cover to cover, they get close enough for tandem knife-fights to break out. The bar-brawl like chaos ensues as the last of the Security force fires from the windows, hitting an anti-shock troop and killing him. The attackers are down to two members, and rush madly to the bridge. Only one makes it through the hole in the wall, but none reach their objective. The last remaining Security member is the last man alive in the entire sector.