I will be making this simple.
Hope u all dun mind.
The following common boss are of the following:
MUSHMOM
Spawn rate:30-60 min
Location:Someone Else's House
ZOMBIE MUSHMOM
Spawn rate:45-60 min
Location:The Grave of Mushmom
JR BALOG
Spawn rate:4-6 hours
Location:The Cursed Santuary
BLUE MUSHMOM
Spawn rate:23 hours
Location:Hall of Mushroom
MALE BOSS
Spawn rate:10 second to 10 min
Location:Armoury
Showa Street 3
The Nightmarish Last Days
GRIFFEY
Spawn rate:3-6 hours
Location:Griffey's Forest
MANON
Spawn rate:3-6 hours
Location:Manon's Forest
PIANUS(left)
Spawn rate:36 hours
Location:The Cave of Pianus
PIANUS(right)
Spawn rate:24 hours
Location:The Cave of Pianus
BLACK CROW
Spawn rate:23 hours
Location:Encounter with the Buddha
FEMALE BOSS
Spawn rate:5-8 hours
Location:Parlor