Moon Princess – it depends on which “helper” character you have on the right hand side of the screen. The red one (Love) is the one that changes the symbols. Just think of it as the “barrels” in Blueprint’s King Kong Cash. A load of barrels appear on the screen and when the reels stop, the barrels will reveal a symbol. That’s what Love seems to do. I definitely helps to read the paytable though.
Sweet Alchemy – I’ve not seen this, but if it’s anything like Moon Princess (Bejewelled / Candy Crush type game), then I’m guessing it’s colours or characters-based again.
Reactoonz – what happens will depend on the colour of the bars on the tanks. Each colour has a different modifier. I don’t know which is which by heart though, so again would need to read the paytable.
Falcon Huntress – this one, I genuinely don’t know why connecting symbols don’t always expand.