If you activate Mirror Entity's ability to give all your creatures all creature types, can you then search for any creature in your library using Sliver Overlord's ability?
I understand that you don't "control" your library, but you do control cards on the battlefield and stack. But when you search your library, does it not become part of your stack, or at least doesn't the card you find in it?
Btw I stated "cards" because I know the word permanent means something else.