Oracles and the Templar boss follow on from opening the Vault is split into three sections, which demand escalating levels of coordination between the six players on your fireteam in order to make progress.
It may take a while to get your head around everything and you will probably get wiped out a few times before it becomes second nature. With a bit of practice, though, you will wonder how you ever found it so difficult.
Defend the Confluxes
This phase of the fight is itself split into three stages. You're going to be defending Confluxes - those spindly white towers of energy - against waves of Vex who will try to get through and sacrifice themselves. Too many sacrifices and you all wipe and have to start again. First of all you defend the middle Conflux, then left and right, then all three at once.
The key enemy to watch out for is the Fanatic, a glowing suicide bomber who will race towards you and then erupts into a pool of green goop upon death. Stepping into these pools gives you a mark - a message appears in the bottom left of the screen - and if you don't remove it by jumping into the cleansing pool at the bottom of the stairs in the centre of the battleground, you will be killed the next time the Templar uses its Ritual of Negation. The best thing to do, then, is not allow the Fanatics to get anywhere near the areas where you do most of your moving around.
Before you begin, divide yourselves up into twos as you did outside the Vault, making sure your best players are evenly distributed. For the first stage, two of you go left, two middle, and two right. Enemies will emerge in all three zones, giving you a sense of their spawn points, where you should try to choke them off as much as possible. Once you have defended the first Conflux and it disappears, watch out for a big wave of Fanatics through the centre.
For the second stage of the fight, the middle team should split up and go help on left and right. There will be a steady stream of Fanatics during this section of the fight, as well as Goblins and Minotaurs.
Once the left and right Confluxes disappear, the mid team should reassemble so you have two players left, middle and right. This is the toughest part of the fight but you should know what you're doing by now. If you find yourself getting overwhelmed at any point, call it out on voice chat and quickly reinforce positions. A few Vex sacrifices won't be fatal, so don't waste your life on lost causes, but do try to avoid massive overloads in any area. Once the final set of Confluxes disappear, another wave of Fanatics will attack, then you're done.
Destroy the Oracles
Actually, you're just getting warmed up. The second phase of the Templar fight introduces the Oracles, one of the most annoying and important elements of the whole Raid. Oracles are extremely bright yellow lights that chime musically when they appear and need to be destroyed immediately or else your entire team will be marked for negation. There will be a cleansing pool in the centre of the arena as usual, but you can only use it a certain number of times before it disappears.
There are seven Oracle positions around the arena, which are demonstrated for you at the beginning of this phase of the fight. At first a single Oracle will appear, followed by a wave of enemies. Then two will appear close together, followed by a wave. Then three, four, etc. There are seven waves in total.
Each Oracle actually has a slightly different chime, so in theory you can use this to work out which one just popped up, although in practice you need to distribute yourselves around the arena and keep your eyes peeled, then call out Oracle positions when they appear.
There are a couple of ways to approach this phase of the fight. One is to put your best player in an overwatch position with a sniper rifle at the back left of the arena, giving him or her clear line of sight on four of the Oracle positions, ideally guarded by someone with a big gun who can keep an eye out for Minotaurs. The rest of the team can then monitor the other three positions and mop up Goblins and other enemies in between.
Another way is to continue splitting your team up into twos and patrol left, mid and right, sending reinforcements as and when necessary. This is simpler if you're new.
However you approach it, your number one priority is to deal with the Oracles. Fail at this and the whole thing descends into chaos and/or you wipe. Priority two is Hobgoblin snipers, who will start spawning (and spawning and spawning) on elevated platforms situated at the outer reaches of the battleground. Everyone must keep moving around, even if you're dealing with a static target like an Oracle, to stand a better chance of avoiding their sniper rounds, and if you're splitting up into sub-teams of two, make sure to communicate any Hobgoblin sightings or, better yet, deal with them yourself.
Once you've cleared up the enemies at the end of the seventh wave, you should get a loot drop, potentially including weapons and armour, before you take on the Templar boss.
How to kill the Templar
Finally it's time to deal with the Templar itself. This giant Hydra-style enemy is surrounded by an impenetrable forcefield that you need to take down using the Relic, another important element of the Raid that gets its first airing in the Templar fight. You can only damage the Templar when the shield is down.
Begin by nominating someone to use the Relic, which spawns at the bottom of the stairs in the centre. This role is critical but the Relic itself is very powerful, allowing the holder to deliver devastating melee attacks, so it needn't be held by your best player. The key thing is that the Relic user is a good communicator, because they need to let you know when the shield is going down and may need to stay on top of cleansing.
The Relic has several capabilities. Like the Sword of Crota, it is constantly charging its Super at an accelerated rate, and it is this Super attack - activated in the usual way using both bumpers at once - that fires off a blob of light that brings down the Templar's shield. The Relic also has light, heavy and aerial melee attacks - the latter bringing you down to earth with a thump that delivers hefty splash damage.
It also has a critical defensive capability: cleansing. Holding the left bumper (usually the grenade button) activates a bubble that removes the negation mark from you and anyone else it touches. Be careful, though, because cleansing has a cooldown.
Once the fight starts, the Relic holder needs to let everyone else know when the shield is going down so they can pile in on the Templar. Don't fire rockets immediately, though, because once the Templar shield goes down a few of you will be randomly encased in a shield bubble summoned by the boss, which you need to shoot your way out of before you can start firing at your enemy. Once clear of the bubbles, everyone should lay into the Templar.
While all this is going on, Oracles will start spawning in the seven locations from earlier on in the fight. Keep calling them out and dealing with them, although remember that it doesn't matter that much any more because the Relic holder can cleanse you when you're marked. In fact, if you remain bunched together you can ignore the Oracles entirely and rely on the Relic holder's cleansing to keep you safe.
When you find the right rhythm with the Templar, you will start taking him down pretty steadily. It's a good idea to make haste, too, because if the fight lasts too long then the Templar will become enraged and start summoning loads more reinforcements. Try to kill the Templar before it reaches this stage, and watch out for its teleportation evasions.
Once the Templar is down, take a moment to compare loot drops. Dancing is also appropriate.
It might seem obvious where to go next, but there are actually two paths forward. The first is through the big door in the centre of the area. The other is a side passage that leads you straight to one of the loot chests in the next area, the Gorgon's Labyrinth. To find this, look for a gap in the right-hand wall on the stairs that run up the left side of the arena. There's a standard Venus chest inside, then a tunnel you can crouch through.