The Magical City, New

The Magical City, New enters the battlefield tapped.
{T}: Add {W}, {U}, or {R}. When this mana is spent to cast a legendary spell, put a +1/+1 counter on this land.
{4}: The Magical City, New becomes a 1/1 white, blue, and red Human Artist creature until end of turn.
The Magical City, New can be your Commander. (Commander tax still applies.)