Add "public release of the tax returns of Donald J. Trump, the Trump Organization, all Trump children and their spouses and any other place that Trump money might be hiding" to the list of official acts that Biden might take here.
The "haha he should use seal team 6" takes are pure fantasy. But this one seems like unequivocally a good idea. Not really escalation given but also would signal he sees that it's not the moment for "when they go low we go high".
(I put scare quotes on "legally" because, though the Trump v. US decision is so badly-written it's unclear, it's probably actually just "with impunity" but that's effectively the same thing.)
Pretty much, he'd need to get a new Judiciary Act through Congress, and good luck with that one. FDR's idea to pack the court was a legitimate threat because he had both houses of Congress on his side. Biden, not so much.
I mean, it would still be illegal, technically, but he just couldn't be punished for it. My other idea is to order Barron Trump arrested, just for the trolling effect it would have. To be clear, release him again in under 24 hours, but make your point.
Barron is 18, and has been involved in some shady shit with Martin Shkreli and "DJT" crypto-currency. No, truly. But the intent would be to simply arrest him for a time, simply to troll everyone. And then make a point that maybe who is on the SCOTUS is important.