This is the only thing I have left for the season. I know the Portals spawn a commander but what other events spawn one?
The one with the 5 tornado things around it, where you have to disable them one by one.
all of them, just complete the events found inside the area of the helltide
The portal mission as you mentioned does, as does the one with a giant tornado in the center. You have to disassemble a series of effigies around the tornado before it clears and unveils the helltide commander.
Northwest of Kyovashad are two event spawn points you can bounce back and forth between to check for the right events. Gea Kul has a similar situation just to its north if I recall.