So here you go. And keep in mind that this is something I'll use in a situation where I'm up against bleeders. If your mission is mostly Temple Guardians, Skeles, Azures and assorted undead, then yes, it's going to be a wasted skillbar. But against bleeders (most of the game), it's excellent. Against onezies like Shiro, #s 3 and 4 might be useless, but 1 and 2 will still fit nicely with other skillbars.
And this is tested in PvE. Whether it would be effective in PvP would depend on how often your opponents group or near each other, how good you are at timing #3, and how smart they are when it comes to #4.
1. Rotting Flesh (Prophecies-only). This is a 2-second cast, the longest of the whole string, but in a PvE situation, you get away with it easily at first aggro -- you don't alert them until the cast hits. And at 2 seconds, you'll land it more often than not in combat. Any longer would be bad.
The point of it is to throw poison onto your opponent. If you're with a Ranger using Apply Poison, it's easier to rely on him for this, but you can't always do so.
2. Virulence (E, Prophecies-only). No, it's not a wasted Elite. This adds disease and weakness onto your poisoned foe, compounding the degen considerably. This is a 1-second cast, rarely interrupted, and a recast of 10 seconds isn't bad.
3. Epidemic (core skill). You've got one person managing the aggro, right? Good, because you nail your opponent with this, and it transfers the poison, disease and weakness (equal durations to your current foe) to every opponent adjacent to him. This is a 1/4 second cast, virtually impossible to interrupt, but the longest recharge of the skillbar (15 sec, which is not at all that bad).
By now, a couple of hits from your truncheon plus all that degen will probably bring down your first foe. That's when you throw down a
4. Well of Suffering (Prophecies-only). This is beautiful AoE that doesn't scatter the enemies like hyperactive weasels. Don't tell Anet. They'll nerf it.
When you select your nearby opponent, he'll probably be nearly down from all the degen. If not, if his health is regenerating, hit him with Virulence once it's recharged, and that will reset the duration, and give you enough time to use Epidemic to spread it again. If an enemy monk manages to remove the conditions, just cycle to the next nearby foe and hit Epidemic again, and you'll throw it all back on him.
If your opponents are not contained in aggro, cycle through and look for an enemy suffering some kind of condition. It doesn't have to be poison, any condition will work (not hexes), and then use the Virulence / Epidemic combo. If there's no conditions about, it's back to Rotting Flesh to generate some. Additional scattered Wells can also be a beautiful complement.
Now, you do this with a maxed out Death Magic attribute (Epidemic uses no base attribute, so you don't even need any points in the Mesmer side... although I prefer to bring some Inspiration Magic skills). You can round out your skillbar as you like. I bring Rez Signet, a powerful heal in Soul Feast (there'll be plenty of corpses, unless you have an MM onside, in which case you can swap out for Ether Feast), Blood Ritual and Leech Signet (awful recharge time, but quick cast and interrupts anything, including Healing Signet). You could probably bring a minion skill if you wanted, but you won't have the time to tend to them and keep them effectively healed.
Okay. Go now. Play. Come back and tell me it doesn't work.
Bet you can't.
