The bit I was reading was this:
L H wrote:Act 3: Glowing Blob - Travincal/Durance of Hate - Magic Immune, also fairly tanky, uses Pounce. They really pose no threat and often they suicide themselves because they will pounce onto your totems, which is instant death for them.
Act 4: Landmass - City of the Damned/River of Flame - Cold Immune, tankiest of the five veterans, uses Earthquake which can ruin you pretty quickly due to not having defense to survive incoming physical damage without minions absorbing attacks for you. They should die quickly from Fireheart Totems without you even seeing them usually, partially because they use the same appearance as a Rampagor

It suggests that the Landmass are easy to kill in saying "They should die quickly from Fireheart Totems". It took about 5 minutes! Also they seem to use SoR not sure if they also use Earthquake. Maybe the latest patch has changed them, dunno, I didn't see anything about that but who knows.
And yes they do look like Rampagors - I had plenty of time to have a good look at them!
BTW this is not a criticism in any way, I'm just trying to understand and see if there's some way to beat these quicker. It says they are immune to cold, and it seems they must also have a very high fire resistance. My merc dies very fast so if yours is what's killing them (with lightning) maybe that's the difference?