Suggestion: SB portal healing
Shatterer has that mechanic (only with a handful of crystals instead of 13 portals). 90% of the group still stands by his right foot instead of helping with the crystals. So, I’m not too hopeful that something like this would result in more participation.
Better if SB drop a big AOE instant kill in area where people stand lazy during portals. Make it hit 5 second after portals arrive. That will make those lazy people start moving. 
Better if SB drop a big AOE instant kill in area where people stand lazy during portals. Make it hit 5 second after portals arrive. That will make those lazy people start moving.
Then they’ll move, and once the attack is over, they’ll shift back. It won’t make them do anything other than move.
There are bound to be some players who don’t have the SB achievement which is basically get rid of all of the portals really fast.
Try getting the map you get on to do that. Low level boss should have someone there who doesn’t have it. And it’s not something that players can get without at least a group of players cooperating.
Killing portals counts toward event completion. Use that when people say that they’d help but don’t want to risk not getting event rewards.
just make it spew dark globs of death just like fire elemental used to spit like 40 fireballs+ lava fonts all over the area at a time at launch