Nightmare Castle

Nightmare Castle enters the battlefield tapped.
{1}, {t}: Add one mana of any color in your commander's color identity. If you spend this mana to cast your commander, it enters the battlefield with a number of additional +1/+1 counters on it equal to the number of times it's been cast from the command zone this game.
When this land enters the battlefield, add one mana of any colour to your mana pool.