Sell all of his stock, and call out the execs publicly.

He could use the infamous antidote clause.

I think that clause has to be administered within a few hours and that time has already passed. It may be necessary to amputate a portion of the company.

Have multiple entities buy shares

I wonder if these could be Tesla, The Boring Company, and SpaceX?

The poison pill will apply to "groups" as well, so don't think that would work

Is this legal?

Pay a lot of money.