The term "Dream Giant Clank" is conjectural. The real name is unknown, and a non-canonical nickname or title is used instead. See the reasons for this title in the "Behind the scenes" section below and/or the relevant discussion on the talk page, if they exist.
Dream Giant Clank's only attack is throwing butterflies, which fly away after hitting the ground, at you. After after a short time, Dream Giant Clank dissipates into butterflies, which, also, fly away. In order to defeat him, keep avoiding the butterflies.