10 seconds overview:

• Valakut, the Molten Pinnacle | Field of the Dead: secret commanders

• Sisay, Weatherlight Captain 's task: searching out legendary lands | payoffs such as Tatyova, Benthic Druid

• fuel snowball by looping fetchlands with the likes of Crucible of Worlds or Life from the Loam

• finish with Scapeshift | Peer into the Abyss + Manabond

more detailed:

Using Sisay, Weatherlight Captain as a landfall commander:

1. get Valakut, the Molten Pinnacle | Field of the Dead into play -> Crop Rotation & Hour of Promise are your friends here but generic tutors like Vampiric Tutor serve the same purpose in this deck
2. for Valakut, the Molten Pinnacle turn everything into mountains using Realmwright, Prismatic Omen or Dryad of the Ilysian Grove
3. search for legendary lands using Sisay, Weatherlight Captain + loop fetchlands using Crucible of Worlds | Ramunap Excavator or Life from the Loam
4. enjoy bolting down creatures with Valakut, the Molten Pinnacle or building an army with Field of the Dead while generating additional value through payoffs such as:
   • Shanid, Sleepers' Scourge
   • Tireless Tracker
   • Tireless Provisioner
5. get the snowball rolling by utilising the tokens from Field of the Dead or Landfall payoffs with cards such as:
   • Jaheira, Friend of the Forest
   • Derevi, Empyrial Tactician
   • -> More mana means more Sisay, Weatherlight Captain activations mean more legendary Lands entering the battlefield
6. close the game with Scapeshift | Peer into the Abyss + Manabond

By playing Sisay, Weatherlight Captain as the commander we can run some sort of "payoff toolbox":

• cards such as Jaheira, Friend of the Forest only work with specific setups
• but Sisay, Weatherlight Captain enables playing one-offs of these effects and tutoring them out when needed

Since this deck doesn't play enough legendary nonland permanents to right away tutor for cmc 3+ cards with Sissay, legendaries for every cmc below are included:

• cmc 1 - Oath of Nissa: starts the tutor chain and isn't a totally dead card
• cmc 2.1 - Valki, God of Lies // Tibalt, Cosmic Impostor: a hatebear such as Gaddock Teeg or Kinan might be more reasonable here, I currently play it just for fun
• cmc 2.2 - Lotho, Corrupt Shirriff: helps to ramp & can generate rocks with Jaheira, Friend of the Forest

Does it work? Yes. Does the power match the price tag? Hell no

Inspiration: https://www.youtube.com/watch?v=NBgNMb3q8Ts