3 guys, each have about 264k hps

One does purple stuff
One does green stuff
One runs around like a madman and throws both

They split up just like slats said - the first guy(purple) stays where he is, the other(green) moves down and left, next to the fountain, and the third guy down and right on the other side of the fountain

They become active one at a time, a few seconds apart.

Basically I set all my guys up just like slats, behind the green guy, below the fountain. I put green immunity up on all my guys

Start fight, go nuts on the purple guy. As you are fighting, pull him towards the next guy (green) so that you are standing right on top of both for when the green guy activates. I have a paladin tank and this let me pick up the green guy with consecrate. Although when I did it with my druid tank swipe worked just as well for snagging him.

kill the purple and green, and then do baxter - baxter CAN be taunted, but he resets aggro constantly, so you can just spam your taunts on your tank to get him to head towards you while you nuke him.

As for the puddles, I simply kept all my guys stacked, and the moment a purple puddle appeared under me I straffed just a bit right. So you just strafe right slowly behind the fountain. Worked like a charm.