demonic pony...? no, it\'s a horse

Flying Cumulative upkeep—Gain control of a land you don't control. (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.) This creature gets +1/+1 for each land you control but don't own. When this creature leaves the battlefield, each player gains control of each land they own that you control.

Each land is a Swamp in addition to its other land types.

Flying (This creature can't be blocked except by creatures with flying or reach.) Nightmare's power and toughness are each equal to the number of Swamps you control.