The Obsidian Tower

({t}: Add {b}.)
{b}{b}, {t}: Put a mire counter on target
non-Swamp land. That land is a Swamp in addition to its other land types for as long
as it has a mire counter on it.
"Its cursed growths would spread across every land,
its tainted waters would seep into the soil, and its insidious will would corrupt all who see it."