Mobilized District is a rare Land card from War of the Spark Promos (PWAR), collector number 249p. Current market price: $0.30, TCGplayer market prices via Scryfall.
{T}: Add {C}. {4}: This land becomes a 3/3 Citizen creature with vigilance until end of turn. It's still a land. This ability costs {1} less to activate for each legendary creature and planeswalker you control.