Spongebob is one of the characters that NEEDED to appear in our world of FNF Games online since he is one of the most beloved cartoon characters in the world, so playing a rhythm game against him can only mean tons of fun, even more so if you are doing it on no less than four awesome songs:
BF Vs Spong, a rhythm battle under the sea!
Whether you have chosen the story mode or free play mode, the way towards victory is the same, which is to reach the end of the songs by playing all their notes according to the charts. So, when you see arrow symbols float and match above BF, press the identical arrow keys.
Be careful not to miss hitting those notes too many times in a row, or you lose and have to start again from scratch. Good luck, enjoy!