Spawn chances for all possible monsters inside building:

• Bunker Spider - 26%
  
• Hoarding Bug - 12%
  
• Bracken - 5%
  
• Snare Flea - 23%
  
• Hygrodere - 14%
  
• Thumper - 7%
  
• Spore Lizard - 12%
  
• Nutcracker - 0.4%
  
• Ghost Girl - 0.5%

Outside

• Circuit bees ~ 15%
  
• Manticoils ~ 50%
  
• Roaming Locusts ~ 35%
  
• Earth leviatan ~ 42%
  
• Eyeless dog ~ 58%
  
• Forest keeper ~ 0%
  
• Baboon hawk ~ 0%

If you’re wondering why the numbers don’t add up-to a 100% on each map for outside monsters, is because the chances of each monster spawning is classified into 2 different groups (Daytime and Nighttime).

if there is a "???" sign next to any monster, this means that it may appear, but I don't know what the chances are, but they are extremely small. (Players experience)

Inside:

• Bunker Spider - 22%
  
• Hoarding Bug - 24%
  
• Bracken - 4%
  
• Snare Flea - 29%
  
• Hygrodere - 9%
  
• Thumper - 7%
  
• Spore Lizard - 4%
  
• Nutcracker - 0.3%

Outside

• Circuit bees ~ 22%
  
• Manticoils ~ 49%
  
• Roaming Locusts ~ 28%
  
• Earth leviatan ~ 5%
  
• Eyeless dog ~ 40%
  
• Forest keeper ~ 1%
  
• Baboon hawk ~ 10%

Inside:

• Bunker Spider - 13%
  
• Hoarding Bug - 21%
  
• Bracken - 27%
  
• Snare Flea - 20%
  
• Hygrodere - 9%
  
• Thumper - 3%
  
• Spore Lizard - 6%
  
• Coil Head - 2%

Outside

• Circuit bees ~ 27%
  
• Manticoils ~ 43%
  
• Roaming Locusts ~ 28%
  
• Earth leviatan ~ 15%
  
• Eyeless dog ~ 3%
  
• Forest keeper ~ 83%
  
• Baboon hawk ~ 0%

Has apparently same chances for each monsters like Assurance

Inside:

• Bunker Spider - 22%
  
• Hoarding Bug - 8%
  
• Bracken - 4%
  
• Snare Flea - 29%
  
• Hygrodere - 15%
  
• Thumper - 7%
  
• Spore Lizard - 3%
  
• Nutcracker - 1%
  
• Jester - ???%
  
• Coil Head - ???%

Outside

• Circuit bees ~ 0%
  
• Manticoils ~ 100%
  
• Roaming Locusts ~ 0%
  
• Earth leviatan ~ 18%
  
• Eyeless dog ~ 48%
  
• Forest keeper ~ 4%
  
• Baboon hawk ~ 29%

Inside:

• Bunker Spider - 21%
  
• Hoarding Bug - 12%
  
• Bracken - 19%
  
• Snare Flea - 13%
  
• Hygrodere - 5%
  
• Thumper - 25%
  
• Spore Lizard - 3%
  
• Coil Head - 3%
  
• Nutcracker - 1%

Outside

• Circuit bees ~ 36%
  
• Manticoils ~ 41%
  
• Roaming Locusts ~ 24%
  
• Earth leviatan ~ 9%
  
• Eyeless dog ~ 20%
  
• Forest keeper ~ 34%
  
• Baboon hawk ~ 38%

Inside:

• Bunker Spider - 15%
  
• Hoarding Bug - 12%
  
• Bracken - 18%
  
• Snare Flea - 11%
  
• Hygrodere - 2%
  
• Coil Head -24%
  
• Ghost Girl - 7%
  
• Jester - 24%
  
• Spore Lizard - 2%
  
• Nutcracker - 26%
  
• Masked - 6%

Outside

• Circuit bees ~ 0%
  
• Manticoils ~ 0%
  
• Roaming Locusts ~ 0%
  
• Earth leviatan ~ 12%
  
• Eyeless dog ~ 49%
  
• Forest keeper ~ 39%
  
• Baboon hawk ~ 0%

Inside:

• Bunker Spider - 15%
  
• Hoarding Bug - 10%
  
• Bracken - 6%
  
• Snare Flea - 12%
  
• Hygrodere - 8%
  
• Coil Head - 12%
  
• Ghost Girl - 4%
  
• Jester - 15%
  
• Spore Lizard - 3%
  
• Thumper - 11%

Outside

• Circuit bees ~ 0%
  
• Manticoils ~ 0%
  
• Roaming Locusts ~ 0%
  
• Earth leviatan ~ 35%
  
• Eyeless dog ~ 48%
  
• Forest keeper ~ 17%
  
• Baboon hawk ~ 0%

Inside:

• Bunker Spider - 13%
  
• Hoarding Bug - 7%
  
• Bracken - 14%
  
• Snare Flea - 12%
  
• Hygrodere - 4%
  
• Coil Head - 13%
  
• Ghost Girl - 6%
  
• Jester - 15%
  
• Spore Lizard - 3%
  
• Thumper - 12%
  
• Nutcracker - 13%
  
• Masked - 5%

Outside

• Circuit bees ~ 0%
  
• Manticoils ~ 0%
  
• Roaming Locusts ~ 0%
  
• Earth leviatan ~ 4%
  
• Eyeless dog ~ 69%
  
• Forest keeper ~ 28%
  
• Baboon hawk ~ 0%

You can also check my another guide about monsters description and way's to avoid them

https://steamproxy.net/sharedfiles/filedetails/?id=3096329026

Added outside monsters spawn chances.

Sometimes players say that they have encountered a monster on a given map whose chances of appearing are 0%, data may not be 100% accurate cause it's hard to calculate. The only way to make them 100% would be to find them from the game files, but i'm not able to do that just like other players. These are the approximate odds of them appearing.

V45 Version
Added Nutcracker and Masked spawn chances
I've never met masked spawned by game but i checked that, and it seems to be spawning on 2 moons so i added them.
Cause of Nutcracker and masked, some of spawn chances for another monsters has been changed. I already changed some of them, but i'll still update this.