1, more control button for Tools (A,S,D,F,G) incoming and allow players to again balance demon and his dark block. 

2, This game will not allow unlimited block dropping, in limited number of block rounds, players have to make more and more coins by keeping blocks area in high risk level. 

3, More and more random options that allow players to control different level on next game rounds, which means players are allowed to face "risk and earn"

In the end, I want to design a situation that players will stay in their flow level, then they will keep playing.