School of Fish is a card that creates two small fish allies for the cost of a single blue energy. This card has no offensive value outside of any kind of unity strategy, but combined with a repeatable bounce ability like Orb of Fluidity or King Matsu, you could quickly flood the battlefield with 0/1 fish blockers. Also, if you don't want to repeatedly bounce it it's good to bench it and use Develop-- this way, instead of two 0AP/1HPs, you'll have a 2AP/3HP along with the bonus 0/1!
Strong against: quality decks, decks with low ally count.
Weak against: quantity decks.