Mary Marvel predates them all, at circa 1940:
Transformation sequence? Check.
Superhuman powers? Check.
Skimpy costume? Check.
Magical origin with mythological ties? Check.
Talking animal mascot? Well, sorta, if you allow for Tawky Tawny.
I was in fact at one time working on a story that crossed her over with Sailor Moon...
-- Bob
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The Internet Is For Norns.
Transformation sequence? Check.
Superhuman powers? Check.
Skimpy costume? Check.
Magical origin with mythological ties? Check.
Talking animal mascot? Well, sorta, if you allow for Tawky Tawny.
I was in fact at one time working on a story that crossed her over with Sailor Moon...
-- Bob
---------
The Internet Is For Norns.