Rainbow Drops are items featured in Kirby's Dream Land 2. While collecting them is optional, it is the only way to complete the game one hundred percent.
There is a Rainbow Drop hidden in one level of each world in the game. Rainbow Drops are always separated from Kirby and company by special blocks that can only be broken with certain abilities and/or animal friends. While the earlier Drops simply require the breaking of their adjacent blocks, as worlds progress the process of attaining Rainbow Drops grows more complex, as certain path turns and ability changes are required.
If Kirby collects all seven Rainbow Drops and defeats King Dedede, Dark Matter will leave Dedede's body and the collected Rainbow Drops will form into the Rainbow Sword (which itself has a Rainbow Drop as its ability icon), the only weapon in the game that can destroy Dark Matter.