Four generic mana, Tap: Transform Matzalantli, the Great Door
It becomes less useful with Kudo or Duskana, but its type line gives it extra homes in a Birds and Beasts theme (Tawnos, the Toymaker or Radagast, Wizard of Wilds)
You'll be slinging spells, sure, but Rootha creates flying Elementals with Haste and power/toughness equal to the highest mana value spell you cast in your first main phase
Choose Beckett if you love detailed subgrades, premium slabs, and chasing that rare Black Label
You can either win through Commander damage by using all of your +1/+1 counters on Omnath, or you can use your blink effects on Omnath as a means of burn or spot removal
Exceptions aside, the basic rules are indeed very simple