You get at:
- Level 21 - Summit’s Gate
- Programmaticon 5 book - Skills: Full - Vector, Math, String, Function, Array, and Object APIs
But you don’t have to own the book to use the functions:
Some of the documentation needs updating / in this case replacing hero with this / and I didn’t try if everything works.
From the topic Use of Programmaticon V's array methods :
Nick: “we don’t document it, but Lodash functions are also available as well”
I tried some of them successfully an some not.
Edit:
Sorry for telling you things you perfectly know : you are one of the fist CodeCombat warriors. Respect! 
-)