Down-Arrow + Mouse, you need to click the Startflag, then you can select a level and you can move you mouse, to move yourself. when you die you need to do that again, i hope i can help u! :)
The way the shapes combine seems to be erratic, which is very frustrating especially when it prevents a combo. Also, sometimes the "s" shapes don't combine at all, or when there are 2 combinations at the same time, only one occurs.
Sorry about that! I will fix it in the next update.