OK, just remember, you need to have an open mind to get what Im saying. Please give it a thought.
The idea:
Phase one:
You start off in a small, non-fortified building/structure.
You get 35 seconds to forge a bunker with pallets. Only pallets. (like, those things you pick up with a forklift)
You can put them everywhere, anyhow, but when the time is up, no more pallets. There is a budget and nothing else to buy.
You can not forge outside the fortification zone.
Phase two:
You re-spawn, inside the fortification zone (building/structure w/pallet reinforcements) Weapons drop from above, so that they dont phaze into an occasional pallet.
Enter the flood. (Yes, flood, alien zombies.)
You can fight your way through one, two or three waves of various flood forms before the pallet reinforcements rebuild themselves and you get a weapons drop.
Phase three (optional):
Use your earned points to buy more advanced forge options and then place them on the map as you please. Trap doors, spikes, sentinel spawn, napalm-mines, you name it.
Every subsequent wave gets tougher and more massive. Eventually we see flood drop pods, flood with greater weaponry, and the true form flood enter the battle.
Could use a public leaderboard that shows who made it the longest and on what map.
And yes, I know it has its similarities with -Yoink!- Zombies, but people have been asking for flood firefight since the dawn of time! (well, maybe since Halo 2)
