Fought this Rhino for nearly an hour and got him only to 93%. It seems you have to shock him out of frenzy somehow but can't seem to get him out of that state easily, or for long enough to even have an effect. Am I missing something?
Run over to the electro thing in the corner there and have him charge that. It will knock him down for a wee bit. Still was a long fight for me even with that.
Problem I had was getting that beast to follow me to the electro thing. Took me almost an hour to kill it, it was aweful!
If you just run over and stand in front of it he will target you, that's the circle thing on the ground, he will charge you and then fall over. That's when you can kill him. Rinse and repeat.
I just did my fifth run for the achievement and it was much easier because of the gear drops from in there and I lvl'd to 125 while running them. I also upped my accession stuff and made sure my merc was getting trained, familiar was was trained etc. The last run went so much faster and I got Rino down in about a 30 min maybe less. I was stoked. So don't give up hope. Make sure when you put on the new gear that drops that you remove the adornments from your old gear and put it in the new gear.