This is just basically what are inside the FM rooms.
1 - NPCS that are useful
2 - Snails
3 - Slimes
4 - Extra Bs
5 - Iron Hogs
6 - Empty
7-11 - Big Foots - Good for RBing
13 - King Slimes
14 - MushMoms and 1 King Slime - Good for Farming Mesos
15 - Balrogs
16 - Crimson Balrogs
17 - Frankenstein
18 - Spawner
19-21 - PvP
22 - Spawner
Hope this helps
1 - NPCS that are useful
2 - Snails
3 - Slimes
4 - Extra Bs
5 - Iron Hogs
6 - Empty
7-11 - Big Foots - Good for RBing
13 - King Slimes
14 - MushMoms and 1 King Slime - Good for Farming Mesos
15 - Balrogs
16 - Crimson Balrogs
17 - Frankenstein
18 - Spawner
19-21 - PvP
22 - Spawner
Hope this helps