talmud gemara - Explanation of Avos 2:6?

Is there a comprehensive explanation of Avos 2:6?

אַף הוּא רָאָה גֻלְגֹּלֶת אַחַת שֶׁצָּפָה עַל פְּנֵי הַמָּיִם. אָמַר (לָהּ), עַל דַּאֲטֵפְתְּ, אַטְפוּךְ. וְסוֹף מְטַיְּפַיִךְ יְטוּפוּן

1. Why is it in Aramaic?


2. Why is this lesson included in Avos (seems out of place)?


3. Who is this skull and how does Hillel know it was drowned due to drowning others? (I have seen many citations that say it was the skull of Pharaoh and source the Arizal, which I have been unable to locate)



4. Why was only a skull found (is there some symbolism specific to the skull)?


5. Why add the word "v'sof" - וְסוֹף?