Back in the 2000s, Retro Studios apparently worked on Mario and Zelda games that focused on the characters of Boo and Sheik. This is what the Shakesparkers report, based on the concept art they acquired in the former Retro Studios producer's former artist portfolio Sammy Hall. The concept art came from the pre-production phase of two plays, back when Sammy Hall was working at Retro.
The concept art from the canceled Zelda project, owned by Sheik, from 2005 to 2008. Apparently, this art provides a "fantastic origin of the Master Sword story" set in Ocarina's timeline of the end of Time. The game, which it never did before the original production, would have been an action / jrpg title "that will explore Sheik's final journey while Dark Gerudo presents Ganon with his 100th birthday". As for the Boo project, there isn't much detail. Art is available from 2006 and 2007. Hall mentions “little things with small solutions” in one of his paintings, suggesting that the game will be on the Nintendo DS. A map of the world was considered, along with “administrative powers” and “Festivals”. You can see the photo gallery and other concept art below.