Rocktor

The Rocktor is a plug-bug that dwells within holes and tunnels, to block entrance into them.

=In fanon games=

In Pikmin X: Deep Freeze
In Pikmin X: Deep Freeze, Rocktors can be found blocking tunnels that Pikmin can dig through, and will try to scare off Pikmin by scattering dust and stones that send them into a panic. When Pikmin get too close, it simply retreats into its burrow and covers up the hole with its crystal helmet, which Rock Pikmin can shatter to leave it stunned for a few seconds.

In Pikmin: Shadows of the Future
The Rocktor is a strange worm-like creature that wears armor made of rock and lives inside cave entrances. A cave that is plugged by a Rocktor cannot be entered until the creature is defeated. The rocktor, if approached, will periodically cover its den with its rock helmet and scatter stones around by shaking itself. The stones will deflower and push away Pikmin that get hit by them. When defeated, the Rocktor's helmet shatters and the creature itself falls into the cave below, allowing access to the cave it was blocking.