Chaos Space Marine codex. They are tough and they can deal a lot of damage as well. This Unit Review will go over how to use this unit effectively and how to handle them if you are going against them.
Playing Plague Marines, starts with either taking them as scoring or non-scoring units. There are two ways to go about making these guys scoring, first Typhus and he is very expensive, the second and cheaper choice is a Chaos Lord with the Mark of Nurgle. Either way you are getting Plague Marines as scoring units. As scoring units this gives you the ability to take objectives and of course contest them easily. What makes them so good at scoring or contesting an objective? Few factors there one is Fearless, these guys aren't breaking and running away when they lose a few buddies. Toughness 5 is preventing Strength 8 weapons from doubling you out, might ask why does that matter? Because Plague Marines get Feel No Pain, and these reasons are why they are arguably the best unit in the CSM codex.
Building the unit out, just because you can go to 20 marines in a unit doesn't mean it is a good idea. In larger unit the survivability goes up but your mobility goes down. I try to keep it between 7 to 10 with one of them being a champion. We still have options for Rhinos for transport if needed (in those rare cases you need them) and we can still hold an objective and soak up the shots. Specialist weapons; I recommend the dual plasma guns. If it Get's Hot you have a save and FNP to keep you alive, if you need to pop anything but AV 14 you can do so. In some cases I have been known to use meltaguns but they are limited in range. Rule of thumb if you are aggressive and are moving them across the board feel free to take the meltaguns if you are staying back and holding an object take the range and use plasmaguns.
Now how to build out your Chaos champion, things to remember you have to initiate a challenge, with that you have to drop your opponent and fast. Plasma pistol is an upgrade but save the points it is not worth it stay with the bolt pistol. Naturally you are going to want a power weapon, and with any other Chaos Space Marine champion the end all be all power weapon would be the power sword, but that doesn't help us as much. Since Plague Marines are I3 you are not striking before or equal to any MEQ, so ditch the power sword and put some points in to a power fist. True you are not getting the extra attack when you charge and you are hitting at I1. On the other side of that not much is going to survive you slapping them with your goon hand. If you need to open a vehicle not much stands in your way. Melta bombs, with the release of 7th Edition vehicles are a bit tougher than before, these are 5 points but if they can stop a Imperial Knight from stomping your army in to the ground it is well worth the investment.
So we have the basics down on how to build a unit. The two best ways to use Plague Marines are to stay back and hold objectives or charge forward to hold an objective. They don't fair well charging in to an enemy unit, you will tar pit the group and take a bit to grind them down. Sure with monstrous creatures you could tar pit them and grind their hit points down, but that isn't optimal in most cases and the creature will slowly die to the plague knives. With Plague Marines I enjoy sitting back hold the objective and wait until your opponent charges in. This works great if you are holding an objective not in your deployment area. With objective in your deployment area holding back your Plague Marines to later in the game to come in and hold an objective is a good tactic if you can afford to hold them out for a few turns.