From the Super Mario Wiki
Clusters are floating crystal enemies in the game Super Mario RPG: Legend of the Seven Stars which are found in the Coal Mines. They never fight alone and always travel with other monsters. They are strong against jump attacks and related to another crystal enemy, Pulsars. Both names are also references to astronomical objects; in this enemy's case, it is named after star clusters. During battle, a Cluster shatters itself into fragments, revealing a small smiling creature that is covered instantly by the crystal pieces, rebuilding Cluster's first form and attacking then. His signature move, Psyche!, allows Cluster to defeat its enemy immediately, although once this move is done, the monster self-destructs.
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