All of them. Starting with syntax changes or type hints.... (Python should be always and only be duck typed forever as designed by God itself (it's creator).
No, mypy existed before the type hints spec, and was created by Jukka Lehtosalo; Guido did, once he encountered it, work to make sure mypy could work with Python rather than being a separate, python-like language, and the type hints spec was a big part of that.
Isn't Guido the one who came up with type hints spec and made the reference implementation (Mypy)?