cinnabun_ wrote:They also have their own key configs set
When KEYCONF lumps are included with weapons, they're typically used to assign slots to weapons. However, they tend to conflict with each other and cause some problems. So, delete those KEYCONF lumps, and edit each weapon and assign it a slot through the use of
Weapon.SlotNumber property. More info about weapon slot assignment is
here.
I also noticed that whenever I spawned in the custom monster, it showed up as an error but still attacked and made sounds.
It sounds like the sprites of the monster aren't loaded properly. If the sprites are in a WAD, make sure they're between SS_START and SS_END markers. If, however, they are in a PK3, they need to be in a directory which is called
sprites.