Shelldock Isle is a rare Land card from The List (PLST), collector number LRW-272. Current market price: $2.82, TCGplayer market prices via Scryfall.
Hideaway 4 (When this land enters, look at the top four cards of your library, exile one face down, then put the rest on the bottom in a random order.) This land enters tapped. {T}: Add {U}. {U}, {T}: You may play the exiled card without paying its mana cost if a library has twenty or fewer cards in it.