Joy Butterfly

Joy Butterflies are blue butterflies that appear as a result of certain Kinstone fusions in The Minish Cap. There are three different joy butterflies to catch, which will each either increase Link's speed in shooting arrows, digging, or swimming.

Joy Butterflies are small and slow and therefore are easy to catch. Link can just walk over them to catch it.

Trivia
Joy Butterflies could be a reference to the fact that, in The Wind Waker, Joy Pendants are shaped like butterflies.