SCALES is defined twice in basegame_custom_overrides.json, resulting if the following error:
ERROR : src/main_menu.cpp:929 [bool main_menu::new_character_tab()] Error: SCALES (mutation_branch) has two definitions from the same source (sly_mutation_improvements)!
Fix:
Change line 106 to "ugliness": -1
Delete lines 149-158
LUPINE_FUR is also defined twice in basegame_custom_overrides.json
They are identical, so one copy can just be deleted
SLEEK_SCALES has the same issue, with the same solution.
INSECT_STINGEWR has the same issue in basegame_mutation_custom.json
The two copies are not identical, with the second copy missing "changes_to": [VENOMOUS_STINGER" ],
The second copy should be deleted
VENOMOUS_STINGER has the same issue. They are identical, one copy can be deleted
Sorry I stopped giving line numbers - I was fixing these in my local copy as I encountered them, so the line numbers changed