I would explain it differently in the comments, not talking about the video.
There are teleport PADS, they aren't portals. You can see most of the pads just looking out, into the event area (so you can count them) and each has some sort of effect coming up from it, like a flame, or smoke, or whatever. There are 4 different type of effects, which emanate from the pads and they represent fire, air, water, earth. By looking at all of the pads, or as many as you can, whichever effect is most numerous is the boss you need to fight. Don't worry about the number of trash mnobs/types and don't worry about aura around the boss, that is merely to help you identify as well as look cool.
Once you start taking health from the boss, the effects from the pads will vanish until that boss dies, at which point, you need to count them all anew. I was confused because people kept saying "portal" when they should have said "pad". You go through portals, you step on pads. 5 second check online...
Portal
a doorway, gate, or other entrance, especially a large and imposing one
Pad
flat-topped structure or area used for helicopter takeoff and landing or for rocket launching
Edited, May 25th 2023 6:00pm by hotrod