Many people like myself play MvM ghost town, usually because of the high amount of credits each player begins with (OR because they are bored... like me sometimes...). However, the downside is that there are sevral crit boosted bots and giant bots throughout the wave, not to mention the spy-tank subwave. I am here to teach you the strategies, weapons, and upgrades to use when playing this wave as my personal favourite class, the pyro.

The most important things in this wave are weapons and upgrades. I'm not gonna tell you what to use, but I do have some I would recomend, and some I would not recomend.

PRIMARY

1. Flame Thrower
Now, these weapons (Stock, Rainblower, Nostromo) have no downsides. The stock and reskins are great weapons to use, especially if you have an australium, killstreak, or botkiller one to show off and make people jealous.

2. Degreaser
The degreaser in MvM is probably the worst thing to use. The weapon has no upsides that are good in MvM and 2 damage penalties, which is bad when damage is the thing you need to do the most in MvM. Grab something else, please.

3. Phlogistinator
Great weapon to use on everything. The mmmph meter allows crits which are amazing against giants and tanks. I've nicknamed it tank buster it's so good. I would like to point out however that for all flamethrowers you should upgrade your defenses or atleast your health on kill, and stay away from damage when activating the mmmph meter. Overall an excellent choice for wave 666.

4. Backburner
This is my weapon of choice in MvM. I use it because, similair to the phlogistinator, it has guaranteed critical hits. However, unlike the phlog, the backburner can airblast(Though it costs more ammo than the stock airblast). This reason alone can be a lifesaver in the second sub-wave with the medics and giant critical soldiers, as reflecting rockets can be helpfull for taking out uber medics without "popping" them, or when pinned in a corner by atleast 1 soldier blasting crockets at you.

SECONDARY

1. Shotgun
The shotgun is nonetheless an amazing weapon anytime anywhere anytime. Enough said

2. Flare Gun/Manmelter
Do I need to say anything other than yes?

3. Scorch Shot
I had to edit this because of the recent buff. We had 2 pyros using this item once and beat the wave.

4. Detonator
Good to use when there are groups of robots because you can detonate flares

5. Reserve Shooter
Unless you are a pro airblasting peeps in the air, I wouldn't use this.

MELEE

1. Stock, Reskins, Axtinguisher, Postal Pummeler
Well you probably won't use your melee weapon much in MvM, but if you do, I would recommend any of these.

2. Homewrecker, Maul
Use these if there is an engineer on your team to remove sappers, especially during the spy-tank subwave.

3. Powerjack
One of my favourite weapons in any gamemode. In MvM though, this item allows you to move 15% faster when you are holding it. This upside is helpful in countless situations, from going to get upgrades between subwaves or to get to the battlefield faster. It also makes you take more damage while holding it, but by simply buying a few resistance buffs that shouldn't effect much. I'd recommend this weapon any day of the week.

4. Back Scratcher
This weapon is one you should definately use if you don't have a medic on your team. More health from packs and less healing from your medicine woman (If you HAVE a medicine woman that is) is a great upside, but then it is even better because you do more damage. This can be a life saver.

5. Neon Annihilator
Like the maul and the homewrecker, the neon annihilator can remove sappers from robot spies, however it doesn't do as much damage as the other 2, meaning it takes longer to remove sappers. However, the neon annihilator will crit jarated or mad milked robots, so it's kind of like the bushwacka for pyros. Good choice depending on your playstyle.

6. Third Degree
This weapon is very good during the second subwave. Get a couple of uber or crit canteens to take out the medics, while also damaging the soldiers.

I usually use this loadout

Like weapons, upgrades can change a game in the blink of an eye.
At the beginning of the match, I would recomend upgrading damage, health on kill, and ammo capacity. You should have lots of credits left to spend. Don't spend them on your secondary or melee, spend them on your defenses. I purchase 2 blast resistance, 1 bullet resistance, 1 health regen, 3 crit resistance, and 2 fire resistance.

Later in the game you can get what you want, but I get rid of my flame resistance to turn it into bullet resistance during the soldier heavy sub-wave.

This is probably the most annoying thing ever known to mann. Most spies try to be inconspicuous, these guys are the opposite. They come in large hourdes, distracting everyone while the other spies backstab you. I would recomend upgrading jump hieght and jumping onto a tank and destroying it. Don't worry about bomb carriers deploying anything, as the only bombs for this subwave are in the tanks.

The wave consists of 8 subwaves
1:Bonk Scouts, Pyros, and Giant Demoknights
2:Crit Boosted Giant Soldiers and Über Medics
3:Heavies, Soldiers, Giant Heavies, and Giant Soldiers
4:Tanks and Crit Boosted Scouts
5:Giant Rapid Fire Demomen, Demoknights, Tank
6:Buff Banner Direct Hit Soldiers, Giant Deflector Heavies, and Giant Quick-Fix Medics
7:SPIES AND TANKS
8:Crit Boosted Robots (Bowmen, Soldiers, Demomen, Pyros, Scouts, Heavies, and Über Medics), Tanks

You might be asking how the hell you are going to defeat all this without the bomb being deployed once. Well, if you use the right weapons and the right upgrades, you have a good chance. If you take these strategies, your chance becomes greater. For most of the sub-waves you can just run around W+M1 like most pyros, with the occasional stop to get health or ammo, but some of these waves require skill. Like ambushing your enemies, having your team distract them, jump and smack burning bots with an axtinguisher, and using mouse 2.

The first sub wave is easy, just W+M1 all the bots and circle the giants until they die. No biggie.
For the next one however, you need smething called mouse 2. Using mouse 2 to reflect the rockets at the Über Medics or Soldiers, or at your own feet to escape when pinned down. I managed to get a screenshot and the killfeed features some reflected Über Medic kills.
Number 3 is suicide unless you have blast and bullet resistance. If you have them, hide behind the building closest to the cliff the robots come from, and surprise attack them. Hopefully they will be too busy shooting your teammates to notice you critting thier metal behinds. If you did this part well enough your teammates should still be intact. An example of my generous teammates distracting a giant heavy is shown below.
4 is easy as long as someone takes care of all the scouts so they don't deploy the bomb. Engineers putting a sentry at spawn is usually good for this job. Everyone else just has to destroy the tanks. If the tank gets too close get some crit canteens.
5 is pretty easy too, despite what you may think. I good tactic for taking down the demomen is circling them while holding mouse 1. The demomen are not the best at destroying moving targets, so this is a great advantage. Early in the subwave a tank comes in aswell, but as long as a buff banner soldier is on the team you can take the tanks and giants down no sweat. Sometimes using an axtinguisher on burning demomen is usefull aswell.
the first part of 6 is hard if you can't evade or reflect rockets that well. The second part is easy aslong as the heavy is distracted and the medic doesn't unleash his uber.
7 is just the most annoying thing in the world. The only thing I find scary in MvM ghost town. So scary, it got it's own section.
8 is very easy if you have uber canteens or crit resistance. If you don't have any of these I would buy some, seeing that you probably have a bunch of unused credits from all the hourdes of robots you and your team have destroyed. Then you can just go W+M1 your head off and destroy the tank. Use crit canteens if the tank gets too close.

Your teammates are very important. So important in fact, that I made a section of this guide that isn't even related to pyro.
There are 9 classes in the game, each with a way to assist others and kill robots. Here are all of the ways they can assist you.
SCOUT
Milk can help heal you and slow robots
Fan o' War and Sandman can mark enemies for death
they can drink bonk to become invulnerable and attract robot firepower, making them the perfect distraction
Collects money in large radius and gets health from doing so
SOLDIER
Take a moment to thank every buff banner and battalion's backup soldier in MvM.
Beggar's bazooka is the bane of all robots


DEMOMAN
Sticky traps near the bomb hole and the cliff where robots spawn are massive help, especially towards tanks and giants.
Loch and Load marksmen are extremely effective.
HEAVY
Plop a dispenser near him and he becomes a level 2 sentry with infinite ammo
Rage meter can push bomb carriers into holes, thus restting the bomb
They can destroy projectiles
ENGINEER
Sentry gun does a crap tonne of damage to robots
Dispenser heals and replenishes ammo
Teleporter helps us get to the battlefield
MEDIC
Can activate a shield to protect us
Heals and Übercharges us to make us stronger
Can put mad milk on robots to heal us
He revives us after we die
SNIPER
Throws jarate at robots to slow them down and make all damage minicrits
Exploding headshots deal damage to multiple bots
Projectile penetration kills multiple bots in one shot
SPY
Imobilizes and slows robots with sappers
Instakills normal bots
Great for collecting money while disguised

Hopefully this guide has taught you how to be a better pyro in wave 666. It took me a while to become good and I thought I should share my strategies for those who need them. Thanks, and have fun.