A 1/4 for four mana, Urza notably allows each artifact under its owner's control to be tapped to produce one blue mana, providing absurd amounts of blue mana ramp as long as its controller has access to artifacts
As a defensive card, it also shines: keep your guys from dying to removal, or reuse a comes-into-play creature
A player using this 5-color commander might be willing to make deals and can help the table band together if one player is getting too powerful
I love tokens and aristocrats
Your opponents can just kill Rubinia to get their creature back and, as a creature itself, it's more vulnerable than enchantment-based Mind Control effects
Sazhs Chocobo ended up getting its own card, and it fits as the perfect one-drop on the Chocobo curve, scaling in size as the game progresses