Every land drop adds another green mana to the pile, growing Omnath and firing off landfall triggers.
Sets your commander and theme, then adds about 25 cards that fit plus 20 lands. You fill in the rest.
The top 40 of 513 cards that fit

#2,774$13.58Tuan Duong Chu

#6,802$3.79Wayne Reynolds

#4,077$0.74Heonhwa

#2,473$1.35Heonhwa

#1,659$3.46Scott M. Fischer

#2,088$21.44Tuan Duong Chu

#504$1.98Darrell Riche

#9,576$4.55Jae Lee

#663$0.24Eric Deschamps

#327$12.11Winona Nelson

#3,313$5.06Simon Dominic

#693$12.02Grzegorz Rutkowski

#618$19.99Warren Mahy

UnrankedCristi Balanescu

#1,312$1.67Eric Deschamps

#295$0.43Aleksi Briclot

#2,845$25.57Gabor Szikszai

#3,303$19.58

#601$26.39Ron Spencer

#4,151$0.48

#917$25.23Daniel Zrom

#3,501$0.21Richard Wright

#1,128$26.15Allen Douglas

#17,257$0.10Jeff Remmer

#2,373$0.23Jason A. Engle

#240$8.50Jason Loik & Matthew Cohen

#1,721$8.45Tiffany Turrill

#15,326$0.16Paolo Parente

#1,862$0.25Ryan Yee

#1,237$0.28John Avon

#302$29.49Florian de Gesincourt

#5,213$0.23Jehan Choo

#3,044$37.27

#9,292$0.24Constantin Marin

#328$5.82Chippy

#1,889$17.93Ishikawa Kenta

#3,291$0.33Bachzim

#9,161$0.31Canata Katana

#5,911$0.41Zack Stella

#1,595$5.22Nils Hamm