The Keepers of the City will be unlocked at the end of chapter 3 and from then on you can encounter them. They are special enemies with a golden crown icon over their heads and they will hang around until you defeat them. They always drop safe keys.
Special enemies with crown icons over their heads lurk in various places and won't move on until beaten. These midbosses can be tough and you may want to give them a wide berth until you're sure you're up to the challenge.
Assaulitng BatterLevel 33.
Batterer out of HellLevel 31.
Big Endgame HunterLevel 45.
Biker BossLevel 45.
BonsaientistLevel 35.
Crotchety GeezerLevel 32.
Death KnuckleLevel 32.
Death's-headLevel 39.
Edison of AnarchyLevel 41.
Forsaken SamuraiLevel 41.
Ghillie ManLevel 31.
Heavenly HostLevel 31.
Hemlock DocLevel 45.
Invulnera-BillboardLevel 31.
Ironclad ChefLevel 39.
King of ThievesLevel 31.
Massacre MascotLevel 32.
Nicotine LichLevel 32.
Noblesse ObesityLevel 33.
Pornogra-PharoahLevel 32.
Scarred YakuzaLevel 31.
ScarredfaceLevel 39.
SturmwormLevel 32.
The Dark SweeperLevel 35.
Urbane LegendLevel 32.
WeltraiserLevel 39.
Abstracted DefianceLevel 26.
BacchanalphaLevel 17.
Barrin' Von LewdLevel 13.
Big PaybackLevel 26.
Blood ShadowLever 21.
BonecleaverLevel 26.
Captain CruncherLevel 26.
Championship WreckerLevel 17.
Dancing MadmanLevel 17.
Death SentencerLevel 10.
Dojo MasterLevel 24.
Dosukoi GigantesLeve 17.
Dr. CrimsonLevel 26.
ExecutionerLevel 26.
Extermination-kunLevel 21. SM-913.
Golden StatesmanLevel 18.
Gorgin' GourmandLevel 13.
Jaws of DeathLevel 10.
Judgment SprayLevel 26.
King of BlingLevel 17.
Monster MonasticLevel 17.
NamelessLevel 18.
Oiled BaronLevel 16.
PleatherfaceLevel 24.
QuarterwiseLevel 22.
Shadow DiverLevel 17.
SwolympiadLevel 10.
Tank CommanderLevel 26.
Top DogLevel 18.
Tropical StarLevel 23.
Unquiet RioterLevel 10.
Weeping ArchdemonLevel 24.
Angel of MegadeathLevel 37.
ArminatorLevel 42.
High NecromancerLevel 40.
Maneating Loan SharkLevel 34.
Subjugation-kunLevel 42.
The TwisterLevel 33.
The WheelmanLevel 42.
