Each rank has a different level of status protection: minions are mag 1, lieutenants are mag 2, bosses are mag 3, elite bosses are mag 6, AVs are mag 3 and giant monsters are mag 75. You need to surpass the target's protection in order to mezz them. Dominator and controller holds, stuns, confuses and fears are mag 3 (dominators get an additional 3 mag with domination up and controllers get a 20% chance of an additional 1 mag). Without domination, you need to hit a boss 2x (and an EB 4x). With domination up, these numbers are cut in half. AVs can be mezzed the same as bosses when the purple triangles are pointing down.
https://homecoming.wiki/wiki/Protection
https://homecoming.wiki/wiki/Purple_Triangles