A Doubling Season in the Command Zone for just counters on a 6/6 stick with trample and she is pretty good and breakable
Online marketplaces such as MTGPrice, TCGplayer, and Card Kingdom are valuable resources
You can either build around a legendary creature and try to find cards that will complement this creatures abilities (referred as top-down building) or you can build around a mechanic/theme or combination of both that you find interesting and search for a Commander that will best fit to lead the deck (referred as bottom-up building)
this additional Prize card taken by the opponent powers up Charizard exs Burning Darkness attack
Go-Shintai of Life's Origin and Shrines The Go-Shintais, Hondens, and Sanctums are cycles of shrines that all get better with each other and need all colors to be optimized
So, I build in ways to use that mana, whether it's activated abilities of Creatures or Artifacts or X spells to use more mana as the game goes on