Mist Dragon

: This creature gains flying. (This effect lasts indefinitely.)

: This creature loses flying. (This effect lasts indefinitely.)

: This creature phases out. (While it's phased out, it's treated as though it doesn't exist. It phases in before you untap during your next untap step.)

"Across the plains, farmers who braved the mists began to vanish. Most blamed the goblins; none guessed the truth."

—Hakim, Loreweaver