I just had Nth Metal the other day and the were Healing Pools... I thought it might be random but every time they came up, they were healing pools. It was super helpful since myself and 2 other league mates were walking a bunch of lower lvl league mates throught it that were not quite geared enough and were learning it for the first time!
Yeah, I ran nexus the other day and Nth Metal was consistently power pools so I think it may be random as you said. - Petros