Two important points to note for this level: 1 - Do NOT start the level with a double colorbomb 2 - Do NOT use the fish booster. Both of these will lead to the endless liquorice cascade and you will need to abort the level. The yellow candies can be used safely when released by the keys. They will drop a few times, then…
I think OlaAlmalky was referring to a booster you can use to undo a move - for example, if you could have made a colour bomb with a move but accidentally moved the wrong candy, you could then activate the undo booster to unwind the move and put the board back to its original position before the accidental move.