At the beginning of your end step, put a doom counter on this scheme, then this scheme deals damage equal to the number of doom counters on it to the opponent with the highest life total among your opponents. If two or more players are tied for highest life total, you choose one.
When you set this scheme in motion, choose an opponent. Permanents the chosen player controls don't untap during their untap step. When the chosen player is attacked or becomes the target of a spell or ability, abandon this scheme.