>>the prohibition on ex post facto laws would only affect pardons going forward.

That is plainly wrong. A constitutional amendment can say anything. There are no prohibitions.

Well, no, it’s in the US Constitution. So I suppose congress could add a constitutional amendment to remove the prohibition on ex post facto laws. But that’s so unthinkable it might as well be a fantasy. Far from “plainly wrong,” which seems unnecessarily aggressive verbiage.

Why couldn't the amendment just say, "The presidential power pardon is revoked, and all prior pardons are null and void"? You have to amend the Constitution to remove the pardon power regardless, why would it be so difficult to put in a clause saying that it's retroactive?

An amendment can’t violate the constitution. It is the constitution. You can do anything.

> Presidential pardon immunity is unreversable

But presidents are also immune against prosecution for official acts. Could a president just disregard pardons from a prior administration? Immovable object, irresistible force kinda situation right?

Yes, but the courts would dismiss the case. If not the appeals court would. If not the Supreme Court would.

And then you use presidential immunity to Maduro a few justices.

At least 3 members of the Supreme Court are among those working under the current admin who need to be serving life sentences in prison.

If at least two-thirds of the Senate doesn't agree, then that doesn't matter.