Spoilers for this book

Ocean empire: Queen Lizze (missing)
Cod empire: King Jimmy
Mazlea: *the short king* Joel
Overgrown: Katherine (missing)
Rivendell: kings Scott and Xornoth
Grimlands: currently no leader
Crystal cliffs: Gem
Pixandra: king Pix
Lost empire: Joey
Mythland: Sausage
Undergrove: a council (my Idea)
Gilded helanthia: Pearl

(Correct me if I'm wrong but I think these are all the empires and there leaders)