Want to do the Love is in the Air holiday bosses? Short version: don't stand in things.
Longer version, you say? Sure, we can do that. First off, while there is a quest chain that leads you to Shadowfang Keep, you do not have to have done any of those quests to engage the evil Crown Chemical Company apothecaries: there's a helpful NPC, Investigator Fezzen Brasstacks who will give you the quest and items necessary for the fight. Like previous holiday bosses, you'll be able to engage the apothecaries once per player so yes, you can chain in alts and keep repeating the fight over and over again. (I believe we killed them roughly eight times before people started getting sleepy.)
Depending on gear levels, this fight can be somewhat challenging or a complete cakewalk. For starters, the quest that allows you to start the event and turn Apothecary Hummel hostile also grants you two items that trivialize the fight's 'don't stand in X' mechanic and reduces the various apothecaries damaging auras. The 'Perfume Neutralizer is the purple vial that comes in the kit the questgiver hands you: it renders you immune to Apothecary Hummel's damaging aura and all his chemical attacks, including the purple puddles he throws on the ground.
Meanwhile, the 'Cologne Neutalizer' has the exact same effect, save that it works against Apothecary Baxter's green aura and puddles instead of Hummel's purple ones. The final member of the trio, Apothecary Frye, does not have a damaging aura but throws both colors of puddles on the ground. Therefore, with a little awareness it's perfectly acceptable to choose which color of Neutralizer you're going to use once Frye is the only apothecary left and simply stand only in the color of puddles that you are immune to.
We did all of our attempts with one tank. Neither Apothecary Hummel nor Baxter's damaging auras hit for so much that a reasonably geared tank/healer team can't handle them (I'd say if you're in 232 gear or better and use the Neutralizers this fight is easily single tankable, and you might even be able to forgo the Neutralizers and still kill them): simply have the tank pick up Hummel as soon as he comes out of his usual villainous monologue and build some aggro, then as soon as Hummel calls out for Baxter switch to him and get him locked down. By then, Hummel should be reasonably close to dead, so just let whatever AoE threat you have keep Hummel on you while you work on Baxter. Keep Perfume Neutralizer up until Hummel is basically about to die then switch to Cologne and Baxter will prove no real difficulty.
Both Hummel and Baxter have cone AoE attacks that can be avoided by just pointing them away from the group by the tank. If you'd rather, you could have a ret pally, feral cat druid, DPS DK or warrior go slightly tanky and hold Baxter for a few seconds instead of double tanking them, just have them use the Cologne Neutralizer and they might not even need to do more than hit RF, Bear Form, Defensive Stance or Frost Presence.
Apothecary Frye adds a few seconds after Baxter, who is called into action by Hummel a few seconds into the fight. Since Frye has a constant reset to his aggro table and is immune to Chains of Ice or Piercing Howl (at least he seemed to be when I tried those abilities on my DK or my warrior tanking as fury in a mix of gear) it's probably easier to just nuke down Frye as soon as he comes active. We left him for last and killed him first and never really felt that it mattered, he was just annoying enough with his sudden aggro switches that killing him first made for less irritation. Frye resets so much that it's not really worth trying to tank him, but since he has no damaging aura and the majority of his attacks is him throwing cologne or perfume on the ground, just pick a Neutralizer and only stand in the correct color puddles.
Also throughout the fight adds will run into the party and blow up: this damage is unavoidable but also fairly minor, our elemental shaman off-healed the fight with minimal difficulty.
So that's basically the fight. The proper use of Neutralizers turns an annoying amount of AoE and splash damage into an entirely trivial mechanic, and makes this encounter one that can be accomplished by an entirely offspec group as long as they're reasonably geared and quick to not stand in things. Once they're dead, Apothecary Hummel drops a quest item to turn in at your faction capital, various iLevel 226 necks identical to the Emblem of Conquest ones, and a chance at some rare items including the infamous Love Rocket.