Entropy needed Genis' help to kill Eternity.
But Entropy re-created Marvel on his own (well, by getting shot in the face by Genis)
I say he re-created Marvel (not just the Multiverse)
because according to Marvel.com,
that instance was one of the 4 times Marvel has ended, and then been remade,
due to 616's involvement in the destruction.
Of course, it was only the Prime Multiverse Genis & Entropy erased but,
as we know, take out the Prime Reality, (616)
and everything else collapses in a chain reaction.
(they took out the entire Prime Multiverse, which houses the Prime Reality 616)
I will submit though,
the arc makes it seem as though
Genis did most of the work concerning the destruction of Eternity.
While Entropy obviously did most of the work concerning Eternity's re-creation.
This isn't too surprising,
Songbird & Zemo saw the Future
where Genis erased every Timeline (Tinny Universe) connected to the 616 Reality,
including the 616 Reality itself.
This he did, on his own.
This is why Genis allowed himself to be killed by Zemo.
