Slug Great Division

Katsuyu, being a mollusk, has a body that is naturally difficult to grasp hold of, in turn granting it a natural defence. As an additional defence, it can, when it's being physically attacked, divide its body into countless smaller versions of itself, thus nullifying the attack. The smaller divisions, each one a full-functioning Katsuyu, can recombine when they wish, restoring Katsuyu to its larger size. If a Katsuyu should be attacked again, it can just divide again, repeating the process indefinitely until the attacker gives up.

Even without being attacked, Katsuyu can create divisions of itself in order to cover a large area, with each division carrying out different tasks, as is done with Katsuyu: Immense Network Healing.

Trivia

 * This technique is an exaggerated version of a slug's autotomy, where it self-amputates part of its tail to escape predators.