First off, Sidisi is a placeholder for the generic BUG 2/2 Legendary Creature for the format.

There are two main ways to win the game:1. Oath of Druids2. Doomsday

The turn after you cast the Oath of Druids, you want to trigger it, either through your opponent just having > 0 creatures naturally or through Forbidden Orchard, milling cards until you hit Laboratory Maniac. The next turn, you mill the remainder of your deck in your upkeep and win through the Maniac during your draw step. There are a bunch of options for your stack of 5 cards, but the main principle is something along the lines of Gitaxian Probe -> Predict -> Laboratory Maniac -> Unearth -> Cantrip. If you have a cantrip in your hand or a Sensei's Divining Top in play, you can draw into the Probe, use that to draw into Predict, play Predict naming Laboratory Maniac and milling it. Then we draw the Unearth and any cantrip. We cast Unearth on the Laboratory Maniac and then the cantrip to win on the spot.

The deck can also win off of Demonic Consultation or Tainted Pact really easily, although it is only reliable if you already have the Maniac. The Demonic Consultation kill is also aided by knowing the bottom card of your deck, like from a scry.

I'm really questioning the sideboard. In addition to not knowing what would be good to run, I'm not sure if Gaea's Blessing or Elixir of Immortality is better, and likewise between City of Solitude or Dosan the Falling Leaf.