Seeing as the ruling extends to all animals and even to birds (as will be explained in Pasuk 33), why does the Torah mention specifically an ox?
Rashi: Because it is common for oxen to damage in this way.
Seeing as the ox needs to be stoned, is it not obvious that it may not be eaten; so why the Torah need to specifically say so?
Rashi and Rashbam #2 (citing Bava Kama, 41a): To teach us that, even if the owner slaughtered it after Beis-Din sentenced it to stoning, it may not be eaten.
Rashbam #1: The Torah is teaching us here that, even though it permits selling a Neveilah or Tereifah to a Nochri or giving it to one's dog, it is forbidden to do the same with a Mu'ad ox.
What are the connotations of "Ba'al ha'Shor Naki"?
Rashi #1: It adds the prohibition of deriving any benefit from the ox. 1
Rashi: Since in the following Pasuk (in connection with a Shor Mu'ad - an ox that gored three times) the Torah writes "v'Gam Ba'alav Yumas", it needs to write here, that the owner is Patur. 2
Targum Yonason: (If a Mu'ad kills a slave, its owner pays 30 Shekalim.) The owner of a Tam is exempt from this.
Like a person tells his friend 'Ploni Yatza Chinam mi'Nechasav' (So-and so lost everything); he has no benefit whatsoever from his property!' (Rashi). R. Avahu in Bava Kama, 41a, learns this from the words "Lo Ye'achel" (See Ba'al ha'Turim). See also 21:28:2:2.
Hadar Zekenim: Since he knew that it is a gorer, he is Chayav Misah [bi'Ydei Shamayim]. Since he himself did not kill, Beis Din takes Kofer for him. (Here, he is not Chayav at all. - PF)
Rashi writes that the verse needs to forbid if it was slaughtered after it was sentenced, it may not be eaten. Perhaps it is needed for a Ben Paku'a (a fetus in a slaughtered animal), which does not need [another] Shechitah!
Moshav Zekenim #1: If a Ben Paku'a, which was already permitted through Shechitah, becomes forbidden, all the more so a regular ox that was not permitted yet! We learn the smaller Chidush, but a Ben Paku'a, or an animal slaughtered before the verdict, is not forbidden.
Moshav Zekenim #2: Also a Ben Paku'a is forbidden in its lifetime, due to Ever Min ha'Chai. 1 Therefore, stoning it is like Shechitah, and it is forbidden.
Moshav Zekenim #3: Even if "Lo Ye'achel" is needed for a Ben Paku'a, or for a bird according to the opinion that the Torah does not require Shechitah for birds, "Es Besaro" forbids if it was made like meat (slaughtered).
Da'as Zekenim: Ben Paku'a is as if it was already slaughtered. We hold that if it was slaughtered before the sentence, it is permitted. 2
Riva: The Torah discusses a Stam ox, and not a Ben Paku'a.
Riva citing R"S ha'Kadosh: If a Ben Paku'a that was stoned becomes Asur, this is due to the verdict (and not because it is Neveilah), so the same applies to an animal slaughtered after the verdict.
Moshav Zekenim: If not, there should be a source that Ever Min ha'Chai is permitted, i.e. in a Ben Paku'a! (I did not find anyone else who says so. Chulin 75b says that if it stepped on the ground it needs Shechitah, i.e. only mid'Rabanan, due to Maris ha'Ayin (Rashi)! - PF)
How does this answer the question? Since we do not need a verse for a regular animal, it should forbid a Ben Paku'a! (PF)
Rashi writes that after it is stoned, it is Asur b'Hana'ah. It should be permitted, for its Mitzvah was done!