mist challenge

Cumulative upkeep (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.) Prevent all damage that would be dealt by instant and sorcery spells. Creatures with flying don't untap during their controllers' untap steps.

Creatures without flying can't attack.

: 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.)