Use the hoarded mana on X-cost monsters, growing +1/+1 counter creatures and multiplying them.
Sets your commander and theme, then adds about 25 cards that fit plus 20 lands. You fill in the rest.
The top 40 of 810 cards that fit

#15,584$0.95Yongjae Choi

#7,889$0.35Jaime Jones

#1,127$5.77Chris Rahn

#6,580$0.13Jonas De Ro

#17,677$0.11

#4,956$2.29Jason Kiantoro

#1,659$3.46Scott M. Fischer

#6,382$0.33

#5,082$0.35Izzy

#917$25.23Dan Hipp

#7,383$0.25

#7,463$5.99Heonhwa

#1,582$34.03

#2,733$0.29Rowynn Ellis

#2,845$25.57Gabor Szikszai

#7,125$8.75

#1,628$3.22Chase Stone

#7,276$0.40Josiah "Jo" Cameron

#1,250$33.86Daarken

#2,428$1.31CatDirty

#3,139$4.43John Tedrick

#7,762$15.05Billy Christian

#5,975$4.48Zoltan Boros

#17,678$0.63

#13,150$0.24

#5,180$0.57

#10,930$0.59Karl Kopinski

#16,179$0.87

#2,472$16.85BODAX

#5,237$1.90Raymond Swanland

#2,515$6.16Kevin Sidharta

#227$63.96Viacom

#186$2.03Abigail Larson

#7,927$0.13Volkan Baǵa

#7,532$0.38

#14,716$0.32Jeff Miracola

#687$9.42Ben Newman

#17,979$0.05Clint Cearley

#14,962$0.33Howard Lyon

#1,225$6.02Matt Stewart