After reading
this post, I started wondering two things:
1. Does the card played by Necromancer get turned over when it's chosen, or after it finishes being played? (My guess is the latter)
2. Does an Overlord being played from the trash stay an Overlord (since it's not in play), or does it get stuck as the card it was played at (since it never leaves play)?
Because depending on how those resolve, then you could do this:
I have two Necromancers in hand. There is an Overlord in the trash, and a Throne Room in the supply. I play the first Necromancer, using it to play the Overlord. I choose to play the Overlord as Throne Room, using it to play the second Necromancer twice. The Overlord is still an Overlord (depending on the ruling for (2)) and is still face-up (depending on the ruling for (1)), so I can choose to use the Necromancer to play it again, potentially picking another card in the supply. When that's done, I turn the Overlord face-down, so I can't use the second play of the Throned Necromancer to play it again.