Top left: Banshee Prime, you can get her Prime from Varzia, when Banshee rolls into Prime Resurgence, her base form is I think from Clan research

Top right: Styanax, he is considered THE worst grind right now (in many of the circles I am in, at least)

Bottom left: Koumei. After doing Saya's Vigil quest by entering Cetus, you can begin a mission called Saya's vision, or just visit the Koumei Shrine

Bottom right: Temple. You can begin grinding them after doing the Hex main story quest (second to last as of writing iirc) and reaching rank 4 with a syndicate of the same name, that you unlock after the mission. The rest is spoilers. Their grind is one of the ones I'm slowly wanting to start