Specter

[TreeTopSky]

{Nightviel Specter} : Can I cast ANY card that is exiled with this card? ie: Land, creatures, instants, etc.

[Splicer]

It says you may PLAY anything exiled. Not specifically cast, so even lands are fair game(just remember, you can still only play one a turn). Basically, the card exiles their cards, giving you both the resources and the spells you want out of thier deck.

[TreeTopSky]

Do the cards go to the player's graveyard upon use? or do they stay exiled?

[Sardok]

They go into their owner's graveyard upon resolution.

[Sardok]

Yes.