A couple of years back (yes, I said *years*), I was farming trash mobs and watched another player use a skill I couldn't then (and still can't) identify. It was a dome that slowed the mobs way down, and you could watch their health bars just drain away. My two skill candidates appear to be Negate Magic (but they were casting it pretty frequently- it didn't feel like an ultimate) and Rune Cage (but this was a skill that seemed to be cast on the ground, rather than one enemy). It was a pretty giant dome and you could round up more than 10 mobs to fit into it.
It was years ago and maybe something has changed or maybe I'm remembering incorrectly, but if it is still a thing, could someone tell me what skill it is?
Thank you!