Activate Mystic Sanctuary and Grim Monolith by tapping them, adding CCC.
Cast Ghostly Flicker either from your hand or from the top of your library by paying 2, blinking Mystic Sanctuary and Grim Monolith.
When Mystic Sanctuary enters untapped, it triggers, putting Ghostly Flicker from your graveyard onto the top of your library.
Repeat.
This clever loop relies on Magus of the Future allowing you to continuously cast Ghostly Flicker straight from the top of your library. By targeting both Mystic Sanctuary and Grim Monolith, Ghostly Flicker resets the land's enter-the-battlefield trigger to place the instant right back on top of your library while also giving you a fresh, untapped artifact to tap for more than enough mana. The combination of Magus of the Future's top-deck casting permission and Mystic Sanctuary's recursive sorting creates an engine fueled by Grim Monolith's excess colorless mana and Ghostly Flicker's reusable targeting.