Yow. Scary amount of mill for, effectively, free. The others in this cycle seem reasonably low poered; this seems a bit too good. (Compare to the classic Mill Stone - this is better in, what, three ways?)

­Nephalia Drownyard has been in tournament-winning decks, and this is about 4 mana cheaper per turn.

Also, that first ability - is it intentional that you can just tap this card itself for the ? Or should this ETBT like Transguild Promenade?

Interesting twist on the "Play only as a sorcery" form of card discard. It's still VERY nasty though, assuming you can play multiple shrines. I think you've managed to build an almost land-only deck. (Maybe add a Sakura-Tribe Scout or similar.)

Anyway - ability is slightly too good (and pure discard lives more often in black than blue) but not much too good. Add an obligatory downside and call it baked.

? This isn't pure discard. This is looting, like on Cephalid Looter or Careful Study.

A land that loots is quite a lot better than a land that scries. This would definitely be played in tournament decks. But (assuming you fix the better-than-Island problem) it's probably printable.

(It'd be printable if it just ETBed tapped. Then it'd compare fairly well to Halimar Depths, but fine on a rare.)