Lauren Faust describing the ponies' maturity level. See also File:Lauren Faust's explanation about main 6 maturity level.png.
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Comments and interviews File:Lauren Faust season one retrospective - Equestria Daily QandA.pdf
I think these might help.
Heeeeyyyy, everybody! It's Meester Tweester! The Hurt\Heal fanfic, now known as Epic Pony War...