The roles in this game can be as simple as trash clearer and large zed clearer but I believe it can go further than this.

-Trash Clearer
-SC Killer
-FP Killer
-Aggro/Puller
-Tank
-Support

If we split these roles up by perk and we look at them individually:
COM - Trash Clearer, Support
SUP - Support
BSK - Trash Clearer, FP Killer, Aggro/Puller, Tank
MED - Support
DEM - Support
FB - Trash Clearer, Support
GS - SC Killer, Support

The one thing that you may notice is that individually, every perk except the BSK has a support role. This means that way one or another, when you see a teammate swarmed by or is about to be swarmed by a massive number of ZEDs each perk minus BSK has the capability to clear them or keep them safe without compromising their position.

If we look at the perks again with team synergy:
COM - Trash Clearer, Support, SC Killer, FP Killer
SUP - Trash Clearer, Support, SC Killer, FP Killer
BSK - Trash Clearer, SC Killer, FP Killer, Aggro/Puller, Tank, Support
MED - Support, Trash Clearer, SC Killer
DEM - Support, Trash Clearer, FP Killer
FB - Trash Clearer, SC Killer, Support, Tank
GS - Trash Clearer, SC Killer, FP Killer, Support

You'll now see that I've added Trash Clearer and either SC or FP Killer to every perk, this is because while individually you may be lacking but with the help of teammates you either have that EMP that goes down giving you clear and free headshots at the SC or due to the way the aggro works you now have to worry about keeping trash off of your teammates. The BSK even picks up all potential categories due to using his EMP for teammates.

These perk definitions however, is not to say how the "player" will be playing them. It is very much viable that a DEM player that knows what they are doing will be solo killing off all 6P SC/FP without any issues (as rare as that may seem).

Let us take an in-depth look into each of the roles next.

Basic Concepts
The trash clearer role is as it sounds, your role is to take out clots/cysts/slashers, gorefast, bloats, crawlers, stalkers, husks and sirens before they have the chance to reach your team.

COM and GS players will want to land as many headshots as possible.
SUP players will want to line up their shots so they can take out multiple ZEDs at once.
FB players just need to shoot the Caulk N Burn, flamethrower or MWG in the general vicinity of the ZEDs.

Due to the nature of FB's weapons, it is advised for FB and BSK to watch a side/entrance so that COM/SUP/GS players have clear views on their targets.

Advanced Concepts
One of the main reasons why teams wipe isn't due to a SC or FP but rather the incoming trash that is piling up behind the SC/FP. This is where as a trash clearer you need to place yourself behind the large ZED to continue clearing trash while the rest of your team focus fires the large ZED.

Here is a video showing myself continuing to clear trash while the BSK pulls the FP back.
https://www.youtube.com/watch?v=ojHo1cYVZmA
At 1:55 you can see an example of pulling, as I keep the 2nd FP aggro on me until the team is ready to engage. You can see when I turn around at 2:12 that the FP was still on me until the team started attacking it. When performing this technique it is very important that you do not pull the large ZEDs aggro. Usually if you go when the BSK is getting attacked, you'll be fine to go behind.

Another important concept as a trash clearer is pushing back ZED spawns and resecuring the original position. This may occur when the team is walking back and back too far to the point where ZEDs are getting instant spawns. Here you will want to push forward and force farther spawns.
https://www.youtube.com/watch?v=Ctvl-lhii5s
In both of these clips, the whole team went for the large ZEDs which started giving the trash ZEDs closer spawns. Noting that everyone was going for the large ZEDs, I push back the ZED spawns to return it back to a neutral position.

Basic Concepts

The Large Zed killer is the primary player that will be tackling the SC/FP if team tactics are not being utilized.

The SC Killer role is left to capable GS players as they have the fastest clearing times solo out of any perk. FP Killers are generally a combination of DEM (stun) + BSK but 2+ GS players are also capable of clearing FP's quite quickly.

Here is a compilation over the past month and a half that I took of playing the GS. Some solo and duo+ kills on SC/FP. More importantly you can watch dandy kill a SC solo while I keep trash off of him at 0:50.
https://www.youtube.com/watch?v=9AFyPN8eGH8

Team Tactics - Utilize when teammates are alive
SC extermination should be done safely with EMP -> team headshots while your BSK still has EMPs left.
https://www.youtube.com/watch?v=kCz_FtKlWks
This works extremely well because the SC's head hp on HoE 6P is 1875 vs his body health which is 5967. The EMP will disable the SC for 5s.

FP should be killed quickly with the help of your DEM player(s).
https://www.youtube.com/watch?v=yHOcrkx-FVM
This is viable due to the stun effect of the DEM nade with the on-perk skill (an on the fly stun against FP). Combined with C4/nade/RPG-7 doing ~1000 a hit (2x C4 without CD adds to about 2k), a single DEM during the stun can chip away 50-60% hp. Just between the DEM and the BSK it is very possible to kill before the stun fades.

Solo Tactics
When there are no EMPs or if your support players are dead, here are some quick kill tactics. Don't rely on these right away if you have a team :

SC : https://www.youtube.com/watch?v=wNTF7cGW8fo

FP : https://www.youtube.com/watch?v=QJ8sQYpgAbs

While mostly a role left to the BSK since keeping aggro goes hand in hand with tanking, there are other perks that can take advantage of holding aggro in order to buy the team some time.

Aggro rules (taken directly from Cat's GDoc):

ZED will not change his current enemy if:
Not enough time passed since the last enemy change time (min - 5s).
New potential enemy already targeted by at least 3 other ZEDs.
ZED currently doing melee attack.
Current enemy within ZED's strike range.
ZED's AI paused.
ZED has LOS on his current enemy and that enemy also closer to ZED than his new potential enemy.

IF ZED can see current enemy and cannot see his new potential enemy.
ZED might change his current enemy if:
ZED does not have LOS on his current enemy.
Distance to current enemy is 20% greater than distance to new potential enemy.

https://www.youtube.com/watch?v=EpF75uGvGZQ
In this example I show how to clear wave 1 in Burning Paris without leaving the main street while there is a SC nearby. The 2nd part of the video shows an in-game example of holding the SC, it's a shame that the SUP player got jealous of our friendship.

I will also add an example of a BSK pull video clip so that you are giving both your trash clearers a position and also to create a 1v1 situation for yourself and the large ZED.
https://www.youtube.com/watch?v=unUxeJgNf8E

When going for tanking, there are four methods that one can use.

First is being stationary and holding block until either your teammates have gotten the kill.
https://www.youtube.com/watch?v=D7vLkcmoTJQ

Second is parrying every attack and continuing to block on unblockables to mitigate damage even further. This is currently not possible due to the guard breaking when you attempt to parry a glowing attack. It is advised that as soon as you identify a glowing parry while stepping back.
https://www.youtube.com/watch?v=Ng_qg6Piv7s

Third is counter attacking on every successful parry.
https://www.youtube.com/watch?v=TWcLu1MSNMw

Last is weaving in and out to avoid taking any damage while counter attacking every opportunity.
https://www.youtube.com/watch?v=pOufK4K7hXs

The Support role can be identified as a Hard Support and Soft Support. Hard Supports can be defined as a perk/player that is not primarily going to be killing trash/large ZEDs but rather making sure that players are cleared if overwhelmed, making sure that they have full hp or providing stun/stumbles when the opportunity arises. Soft Supports can be defined by perks/players that are actively assisting in trash/large kills, dropping EMP and covering your teammate if they need to reload or heal.

COM (Soft Support)
COM is a great support perk as it can keep trash at bay from a distance and doesn't need to move from their position to be able help other perks out. It is a great choice for taking down trash all the way up to SC (as a team). Do your best to avoid fighting FP and instead focus on keeping trash off of your large zed killers.

Here is a video showing some backing up a teammate, keeping trash at a neutral position and going for quick SC decaps.
https://www.youtube.com/watch?v=w_Es_keYLEk
Exclusive to COM : Indirect Supporting - Extending ZT as much as possible. As you can extend ZT up to 5 times, it is important that you take advantage of the slowdown to continue nailing headshots to keep up Zedtime.

SUP (Soft Support)
SUP is a tough class to play overall right now and most likely it will be the perk that will need the most babysitting and money feeding to play efficiently. Buying a HSG in the earlier waves and then going for the AA12 late game is a valid method to play. The best that you could do for your team is spawn blocking and picking off small number of ZEDs. Clear off any teammates that are surrounded by trash and assist in FP's with your nades.

SUP (Hard Support)
If you are looking to go for a full time support role with the SUP then I recommend taking Katana to parry SC/FP, T1+T2 OR AA12 for regular trash maintenance, and MED pistol to heal your teammates.

Overall, I would play the SUP more in a large ZED killer role. It's very possible to play in a support role but it's hard to recommend to do so.

BSK (Soft Support/Ranged)
Playing a support BSK will generally mean that you are not going to be body blocking and spamming M1/M2 at a door. What I enjoy doing is taking a SCAR to keep everything at bay while giving my teammates the opportunity to kill incoming ZEDs as well. When the going gets tough then I will switch over to my melee. Another viable method is having a melee out but just ensuring that you only go out to pick off mediums or problematic ZEDs and clearing trash off of your teammate that you are with.

Here is a video of myself playing a ranged (aka SCARBSK) and having my DEM teammate assist me when applicable. We started doing a combination of Scar/RPG HS for SC and he would stun FPs for me.

https://www.youtube.com/watch?v=sfxL3sOGK58

MED (Hard Support)
As a MED, healing should be the priority before anything else. Nades are good for your tanks and also for clearing out an entryway that doesn't contain SC/FP. Even though it's not MED exclusive, the MED weapons have high stumble and hit power which can be used to stagger (delay) SC's by shooting their legs and cancelling Siren/Husk's attacks.

FB (Soft Support)
FB is very similar to the BSK in that it's more of a killing perk so it's tough to label it with a support role. As with the BSK, you want to clear trash that is getting too close to your teammate.

DEM (Hard Support)
DEM is the second perk that I would consider to be a hard support. The biggest role that the DEM has is ensuring that no FP's ever touch your team. Using the On-Perk skill, stun the FP and in the 3-5s (random) time that the FP is stunned you should be able to deal 5k damage. In that time your BSK or teammates should be able to cover the rest of the 3k dmg.

For SC, if it has not died during the duration of the EMP then try for the impact headshot, if it lands then that is 600 dmg out of a required 1875.

Other than that, you should be clearing your teammate if they are overwhelmed with C4/RPG shots and killing their most problematic ZED.

As of v1013, for the most enjoyment of everyone please refrain from using Nuke. Nuke can bring unwanted raged SC/FP's and will make the match unenjoyable for a lot of your teammates. If the team is not planning on using the current meta, I would not recommend running Nuke.

https://www.youtube.com/watch?v=7_yH6XxLhkg
Note : Do not bother with explosive weapons on SC/Hans as it will only deal 50% damage.

GS (Soft Support)
Just like COM, GS is a great perk to keep trash at bay without needing to compromise their position. Unlike COM though, they are much better suited to SC solo kills. FP killing should not be your main priority however and when possible try and leave that for your FP killing players. While a great perk for SC killing, playing this perk does not guarantee an easy kill. All of us practiced our own methods and got comfortable with one or more methods.

Now that the roles have been discussed, let's take a look at how they play together.

Ideally in a 2 way funnel you would want to have 2 SC killers, 1 FP Killer, 1 Trash Clearer and 2 Support players. My personal preference is 1 ranged BSK, 1 COM, 2GS, 1 MED and 1 Nukeless DEM. This way you have a good balance between constant trash killing with the COM and Scar BSK, GS's firepower for quick SC takedowns, and the ability to stun and takedown FPs quickly with DEM's nade and firepower.

FB's can take the role of trash or large but that should be identified as soon as possible. If they are going for trash then I would place them with the BSK player as the fire effects will generally hinder COM/SUP/GS player's ability to maintain headshots or get clear shots. If you need to be placed with the rifle/shotgun player then do your best to just clear trash that is getting too close instead of attempting to kill the farther ZEDs.

If you've made it this far through my guide then I have to say thank you, I hope that this guide will open people up towards a different approach to teamplay and will help you survive the ZED outbreak without the mindset of getting the most kills.

Thanks to all the players all around the world that have shown me completely different ways of playing this game.

Sima's YouTube | Owner of DEM Guide
Devante
SimpleCat's GDoc[docs.google.com]
DandyBoy66's YouTube
Our favorite fake Russian Polomi
And a final thanks to all my friends.