Epidemius Evaluation

Let's be honest: if we're taking Epidemius in an army list, we want to be playing a lot of Nurgle daemons to the exclusion of almost all others. Unless I'm involved in some Apocalypse madness, Epidemius will only be used in a mono-Nurgle army list. Frankly, he doesn't belong in many other places. That said, let's have a think about how we might use him.

The Tally.
Clearly one of his major advantages is the Tally. We want to get that up to high numbers as quickly as possible. And we want Epidemius to survive during this process. These two wants are in slight opposition to each other. To get the Tally up effectively, we should aim to have Epidemius on the table on turn 1. That may not always happen and sometimes the Tally will get stuffed because he doesn't arrive (or doesn't arrive until turn 4+!).

On the other hand, we don't want Epidemius to demise before his time. And that's a problem because he's going to get targeted. Frequently. And did we mention he's not very fast on his feet (or palanquin)?

Tactics.
Perhaps the best option is to place Epidemius in a moderately large squad of plaguebearers or nurglings. If the game in hand is an objective based one, then just sit Epidemius in cover (hiding) with his squad next to the objective and (preferably) leave him there. The enemy then has to come to you to finish off the squad and target Epidemius himself. And a large squad of plaguebearers is hard enough for any miniature in the game to handle in a single turn, short of a vortex grenade.

Of course, you could always go on the offensive with Epidemius. He is afterall, reasonably good against most infantry in the game. But you'll want to back him up with other Nurgle squads so that if his own squad gets whittled down, he can attach himself to a different (fresher) squad.

Evaluation.
Use in Mono-Nurgle lists or apocalypse ... and planetstrike. He's okay, but an army list needs to be built around him and his powers, whilst simultaneously begin able to cope without him. This means daemon princes with wings and the mark of Nurgle at the very least. A Great Unclean One wouldn't be a bad idea either, alongside a metric ton of plaguebearers, coupled with some beasts of Nurgle and Nurglings to taste. Nurglings especially can be amazing once pumped up by the tally.

I don't use him outside of mono-Nurgle builds though. Unless I'm playing a fluffy game, or a humongous apocalypse game.