Shovel Knight: Specter of Torment

As you complete stages, the tower will become populated with more NPCs. Only certain ones count for this trophy. Most will appear in the banquet hall in the tower. The only one that doesn't is the Rail Rider. The banquet hall is the upper centre room in the Tower. When you speak to each of the required NPCs for the first time, the game will activate an auto save. The NPCs that sit at the head table will always appear there after you complete their associated stage the first time. If you didn't talk to one before it was swapped out for another, not to worry. Whenever you return to the tower the game will randomly select an NPC to place at that table, (only applies if you did not complete a recruitment stage for the first time). You can force the game to randomly choose another NPC by completing a stage, entering and then immediately exiting a stage or backing out to the title screen and reloading your save (I found that to be the quickest). When the last NPC is spoken to, the trophy/Feat will unlock.

Skeleton - Walks back and forth to the right of the head table in the banquet hall. Gives 600 gold. Appears after completing the Plains stage.
Super Skeleton - Sits at head table in the banquet hall, appears after completing the Lich Yard stage.
Dancer - Stands to the left of the bar below the head table, appears after completing the Lich Yard stage. After she dances for you, you will get the Cold Shoulder. (Allows you to strike a pose, required for Spec'd Out)
Tinker Knight - Sits at head table in the banquet hall, appears after completing the Clockwork Tower stage.
King Knight - Sits at head table in the banquet hall, appears after completing the Pridemoor Keep stage.
Goldarmor - Walks back and forth to the left of the head table in the banquet hall. Gives 600 gold. Appears after completing the Pridemoor Keep stage.
Polar Knight - Sits at head table in the banquet hall, appears after completing the Stranded Ship stage.
Rail Rider - Stands in the room to the left of the banquet hall (the room directly above where Specter Knight always starts out from), the room with the grind rails in it. Appears after completing the Stranded Ship stage.
Plague Knight - Sits at head table in the banquet hall, appears after completing the Explodatorium stage.
Minion - Walks back and forth to the right of the head table in the banquet hall. Gives 600 gold. Appears after completing the Explodatorium stage.
Mole Knight - Sits at head table in the banquet hall, appears after completing the Lost City stage.
Birder - Bounces around the screen, starting from the left side of the head table in the banquet hall. Gives 600 gold. Appears after completing the Lost City stage.
Treasure Knight - Sits at head table in the banquet hall, appears after completing the Iron Whale stage.
Propeller Knight - Sits at head table in the banquet hall, appears after completing the Flying Machine stage.