Even if its not, the hybrid mana cost makes it flexible to cast
Agent of the Shadow Thieves Agent of the Shadow Thieves is best for decks with an aggressive strategy involving additional combat steps or an overall Voltron strategy
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
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
As a defensive card, it also shines: keep your guys from dying to removal, or reuse a comes-into-play creature
This is well over the per-pack MSRP of $37.99, and the price may not even stop there