I got it on a treasure goblin, used mark to get hatred back, caltrops to keep it immobilized, preparation to spam caltrops, and entagling shot justice is served. spam caltrops, spam nether tentacles, every 3 hit a single entagling shot.
That can work in pretty much anything that can survive that much nether tentacles without killing you.
Hmmm, seems strange if you weren't able to get it, although sometimes I find some achievements need a few times to get it going: I had to try the one with the fan of knives many times before I got it to activate.
Dual wielding might help if you aren't already if you're having some issue dumping the hatred, but it doesn't sound like you are. I got it completely randomly zoning into Whimsyshire and finding the portal heavily camped, then spamming everything I had trying to live.