Tackling the two door attack
Posted June 15th 2010
Introduction
Near the end of the third floor you get trapped between two doors and have to contend with a mass of Flood spawning from two outlets. It's a nasty situation and seems designed to be the toughest challenge in the whole level. On this page I'll give some ideas for tackling it, including a few challenges for fun.
Attack analysis
First, a few words on how the attack works. After getting a checkpoint near the second door a message on the screen says "Hold your position until the Monitor returns", and around 7 seconds later Flood start spawning from two outlets; initially a trickling of spores but then the first of the combat Flood. There seems to be a fixed delay before the door opens. Measured from that appearance of spores, it's about 61 seconds on Easy, 78 on Normal, 85 on Heroic and 97 on Legendary.
The spawning seems to have a replacement dynamic in which the game tries to maintain a certain number of combat Flood; 4 on Easy or Normal, 6 otherwise. So each time one dies, you can expect another to replace him shortly. However, there seems to be a limit on the total number of combat Flood you get (rising with difficulty level), which means that if you can do a sufficiently fast job of killing them, your allotment could actually run out well before the door opens. Using the fast-killing open defence with efficient use of grenades and shotgun, that can be managed even on Legendary. The allotments look like being around 30 on Easy, 36 on Normal, 44 on Heroic, and perhaps around 55 on Legendary (but the pressure there makes counting too difficult, so that's just a rough guess). If you don't get through the allotment early, spawning will stop when the door opens.
Spare weapons for a flexible save
It's possible to move some spare weapons into the battle area before triggering the checkpoint near the second door. This way you can form a nice flexible save in which you'll be able to tackle things with various weapon combos. Each time you revert, you'll have time to switch weapons if desired. For that matter, you'd even be able to switch part way through the battle.
Hide and wait
You can actually just hide and wait until the second door opens, at which point the few Flood that have spawned will run off to attack the waiting Sentinels. You can hide at the back of the long recess or short recess at either of the doors, or stand behind the pillars between the outlets. All very easy, but also very dull! So dull that I wonder whether Bungie knew about these trivial hiding options. I suspect they intended the Flood to be able to spot you, so you're obliged to fight for your life. As such, I tend to think of the hiding tactic as a bit of a cheat, like taking advantage of a little glitch in the design. It's a boring and totally unchallenging tactic, but it's there if you want it.
Recess defence
Here's what I find the best defence if you're not interested in hiding. Go to one of the doors - preferably the second one - and defend from within the long recess. You've got a great defensive position, with enough leeway for falling well back when necessary.
Shotgun and plasma pistol
On Legendary I favour a shotgun, with either a plasma pistol or pistol as backup - though it's quite possible to survive without ever using a backup. I prefer a plasma pistol as you don't need to reload it and it's better for popping spores. Staying close to the wall for cover, you can use the shotgun to blast enemies as they near the corner or come around it. Try to get them before they fire a shot. If you're at the second door they have to come around a bit further because they have their weapons in their right hands; plus you're right-handed yourself so your gun gets a sight of enemies sooner. Those two advantages are why I recommend defending from the second door rather than the first.
You can also blast Flood as they jump down from the nearest outlet, or even while they're still in the outlet itself; and grenading them at those locations is another option of course. Every now and then, use a grenade to try to take out lots of Flood as they're near the corner, and potentially to buy yourself a bit of recharging or reloading time. Take every spare moment to keep your shotgun reloaded, ready for the times when things get really hectic.
At times you may get forced back deep into the recess by the pressure, and in this case it's good if you've got a frag grenade handy. Try to keep a few in reserve for this. When you use a grenade be very careful to stay well back. There are often loose grenades around and you could get caught up in a chain reaction that you started yourself - and then you'll feel a right fool. In fact, preferably keep an eye out for such grenades and hoover them up as soon as you can to keep things safe. Also try to avoid accidentally tagging a combat Flood or spore, or you can end up with a fizzing grenade heading your way!
Rocket launcher
Rather than having a plasma pistol or pistol as backup, you might be interested in a rocket launcher. It's possible to have a full one if you want. It can provide quick relief in sticky situations, like when you really need to get your shield recharged, but it's dangerous. You'll need to be very careful not to fire it when spores are hopping around in front of you or when combat Flood are getting too close. It's also very slow to reload of course; so if you want to use more than two rockets you'll need to pick your reload time well. It could be a good idea to throw a grenade just before you reload, to try and make sure you won't be coming under fire before you're ready again.
In the past I think I usually took a rocket launcher into this encounter, but eventually I realized I could do better with shotgun and plasma pistol - which also freed me from the concern about blowing myself up! However, the launcher is plenty of fun of course.
Spore trouble
Crucially, don't ignore spores or it could be the death of you! It's important to keep your shield as healthy as possible. Any time you've got a moment's relief from combat Flood, shoot or whack spores to try to keep your area clear. I'd normally be using a plasma pistol for that, but there's usually no shortage of shotgun ammo so don't feel bad about using up shells just to eliminate a few spores. Keep moving around so they find it harder to get you. The most annoying thing about these little nibblers is that they can come up over the abutment you're sheltering alongside, so you can find yourself suddenly getting hurt from the side or rear, and it's easy not to notice that for a while when you're busy fending off combat Flood.
Pillar defence
Between the two outlets is a shallow recessed area with two pillars. The pillars can make for pretty good cover as you vary your attention between the Flood dropping down to your left and right, ideally using shotgun and grenades. There are also a few medkits there, highly useful for emergencies! On the minus side you've got enemies coming from two directions, and nowhere to retreat to. That can make it very hard to recover if things start going bad.
Open defence
Try defending out in the open, forbidding yourself from sheltering in a recess or behind the pillars. In particular you can occupy the area between the outlets, running back and forth blasting Flood with a shotgun before they've had much chance to fire. You can use grenades too (throw, then switch your attention to the other side), and perhaps a few rockets if you've got a launcher. It's a lot of fun.
On Heroic or Legendary you have to work like crazy to stay alive with this defence, but I find that it makes a great challenge. For added challenge you could forbid yourself grenades and just use the shotty. Survival without grenades is possible even on Legendary, though you'd have a really tough time of things.
With the open defence you may not need to bother much with spores because for one thing you're potentially moving around so much that they can't easily get a nibble, and for another, enemy fire is likely to pop quite a few. On Heroic or Legendary you'd be hard pressed to find any time to spend on spores anyway!
Flow-stop challenge
As mentioned in the introduction, this method works fast enough that you can potentially end the flow of Flood well before the second door opens, even on Legendary (though I'd say the sweet spot is Heroic). See if you can manage it on your preferred difficulty level. You can help yourself a lot by including efficient use of grenades, moving to pick new ones up when you spot them. And remember, you don't have to wait for Flood to reach the ground; you can even grenade them while they're still in an outlet. On Heroic I've managed to kill the last of the combat Flood with about 25 seconds to spare before the door opens, while on Legendary I've made it with about 17 seconds to spare.
Up in an outlet
Here's a novel tactic that I consider more a bit of fun than a serious defence. Grenade jump up into one of the outlets. Flood materialize above you and land in front. They'll leap out, not seeing you until they're down on the ground, where you can blast them with a rocket launcher or shotgun or whatever. Of course, you'll also have Flood from the other outlet to deal with, and they'll take a pretty dim view of the proceedings.