I like the effect. However I do not feel like a new rule applied to both players is Entropy's style.
This feels a little too roundabout to fit Fire although it would fits Fire's damage focus.
This might fit Dark because it fights the opponent using the opponent's resources but this also is targeting both players.
This might fit Gravity because it punishes change from the status quo. (Best fit IMO)
This card would be used in decks that do not use cards after a point. As such the effects will probably be lopsided.