Be sure to check your Codex, but I'm pretty sure that only Followers of Nurgle contribute to the tally and only Followers of Nurgle benefit from it. I'm not 100% on that.
But anyway. If you take Epidemius, the best thing to do is to take him as an ally to Chaos Marines. Chaos Marines have a slightly better damage output than Nurgle Daemons. Nurgle Daemon Princes are overpriced and don't have the same hard hitting power that the Daemon Princes in the CSM Codex have. Unfortunately, since the Chaos Marine Codex is so bland and lifeless, and since everyone else has more output for fewer points, I wouldn't plan on winning any tournaments, even with Epidemius. Also, since Plague Marines and Plaguebearers totally suck in assault, I wouldn't bother taking any champions or much of an HQ. Take a single Nurgle Sorcerer and give him Doombolt and then roll on the Telepathy power chart. Then fill your army with Plague Marines with Plasma Guns and Obliterators.
Then cry as your Grey Knight, Necron, Space Wolf, or Imperial Guard opponent blasts you off the table with volume of fire or swanky special rules that you have no defense against.
Honestly, I'd hold off on buying Epidemius for about a month at least, to see what the next month's worth of GW releases are. Chaos Daemons and Chaos Marines are in desperate need of an update at this point.
Joined: Wed Jun 13, 2012 8:30 am Posts: 2211 Location: Planet of the Sorcerers
Basically, as you get kills with models that have Mark of Nurgle that are near Epidemius (not sure if they have to be within range of him, havn't looked at it in a while)
But as you get kills you get really nice effects for everyone with Mark of Nurgle. Ranging from everyone having 2+ poisoned attacks to 3+ Fell no Pain.
That really helps for people trying to do a fluffy Nurgle daemon army. Does it count for CSM with mark of Nurgel or just Daemons. I don't have the daemons dex with me so I don't really know if it specifically says daemons or it just says it generically. If it says it generically and it's not been FAQed then you could use it for plagues and really any CSM with mark of Nurgel.
Kills that happen anywhere on the board by followers of Nurgle count towards the Tally. This affects your and your enemies models.
As i think Epidemus is a great tool for CSM Nurgle heavy lists, it's not the worlds greatest thing. It costs 185 points as you pretty much need to take 5 man Plague Bearer squad to camp with him and this also is needed to fill out the troop requirement for Allies. Hitting the gold of Ignore armor saves takes 20 kills. For you to kill 20 enemy models can take quite many rounds and with a bit of an bad luck your Epidemus won't arrive on first turn or mishaps when he does come. (Daemons can't use CSM Icons btw.)
TBH, i can't say much about how killy CSM units are, but as for Daemons, good ways to ramp up the Tally are Daemon Princes and Ku'gath. Ku'gath gets big pie plate that wounds on 4+ and ignores armor saves. Daemon Princes can actually get to CC and/or shoot with Dread Gaze or Breath. These options are really costly, and i wouldn't suggest them to someone using Daemons as an ally. Also, i'm pretty set on the idea that Epidemus is next to useless in Daemon army as those who really needs his Tally are PB and Nurglings. PB are slow and can't really take that much beating anymore and Nurglings are swarms, so they can't hold objectives and are only usable for tarpitting before Tally ramps up.
PS: We'll see soon what the new codex update in the WD will bring to the table.