On each of the holder's upkeep phases, Chemosh decreases the EC set aside by 0/1. The holder then selects a hero to decrease 0/2. This happens each time, independent of prior choices (that is, you can choose different ones each turn). The decrease happens once for each of the occurrences, and is permanent.
I'm fairly certain that the wording of this card does not allow you to activate it on opponents' upkeeps...but it is an odd wording to be sure...
