Black Dragon Gate

Black Dragon Gate enters tapped.
As Black Dragon Gate enters, choose a color other than black.
{T}: Add {B} or one mana of the chosen color.

Boros Guildgate

Boros Guildgate enters tapped.
{T}: Add {R} or {W}.

{T}: Add {C}.
{2}, {T}: Add X mana of any one color, where X is the number of other Gates you control.

Trample
When Child of Alara dies, destroy all nonland permanents. They can't be regenerated.

Azorius Guildgate enters tapped.
{T}: Add {W} or {U}.