I encounter this demon boss in a cave by the swamp. It is the only one I have difficulty with so far.

At lvl 12 I can't kill it without dying several times in the process, running back quickly from the rebirth fountain before it heals up.

I suspect the black cloud demons it summons are killing me with life leech. I have not seen any significant protection for that at lvl 12. I wish there was a combat log that I could confirm the type of damage being dealt by mobs. Some are fairly obvious while others are not.

I just keep running in a large circular pattern and striking it with hunter /rogue pierce/poison/life leech/energy drain attacks.
I suspect trapping it would not prevent it's summoned friends from attacking me . They are the issue.

Well, he's optional so just don't go in there. He's very hard for most early characters, needs to be toned down a bit I think.

Well I killed Shadowmaw at lvl 12 with my lvl 12 Hunter/Rogue and did not die.

The key was making sure I had extra health bonus equipment and using my hit and run tactic in a straight line to and from the cave exit so as to avoid the life leeching from the summoned minions, and drinking health potions when needed.

Congrats!

He tears me apart. My best effort was a Lvl 13 Warden. It killed him fairly easily. My earliest is with a Battlemage at Lvl 12 but I am 1/2 against him. The Warden is turning out to be a pretty good character. He is now Lvl 20 with no deaths. Tough fights with Alastor, the Minotaur Lord and Megalesios. They never threatened the Warden but he took a long time to kill them. My defense lvl against Alastor was 543 at Lvl 18.