Shumatsu, The Finale

This spell cost {1} less to cast for each
different basic land in play.
You may only cast Shumatsu, The Finale if
at least one players life total is 20 or less.
Shumatsu enters the battlefield with X +1/+1 counters where X is the lowest life total among
players as you cast Shumatsu.
Shumatsu can only attack your opponent with the lowest life total.