Note: This is not meant to be a competitive deck! Especially in Legacy...I don't think this would survive long enough to work.

The main idea is to imprint one of the instants (preferably Manamorphose) onto an Isochron Scepter. Then, get a Paradox Engine into play.

If you imprinted with Manamorphose and you get the engine in play, that's basically game. You can now draw your deck, and whenever you get to a Grim Monolith you can cast it immediately and have then have a surplus of mana as you continue drawing your deck until you kill your opponent with Banefire or Grapeshot.

Alternatively, if you imprinted the scepter with one of the other instants, such as Boros Charm or Lightning Helix, you need to find the Grim Monolith as well as the Paradox Engine, and then you can infinitely damage your opponent once those pieces are in play.

The rest of the deck serves to protect you and help find your combo. The Enlightened Tutor and Bottled Cloister will get you the pieces faster, while Ensnaring Bridge (which is enabled by the Cloister), Grim Lavamancer and Orim's Chant may help keep you alive. Maybe. Maybe not.

Orim's chant can also protect you from countermagic if you play it during your own turn. If you get in trouble you could even imbue it onto a scepter to buy yourself a significant amount of time. This in combination with Ensnaring Bridge can really lock down the game, though ideally the deck works fast enough for this not to be necessary. The Boros Charm's indestructible option can also protect your combo pieces from things like Abrade or even Purify. The Elixir of Immortality helps keep you from decking yourself.

Let me know what you think and any advice you might have! Thanks for reading.