The Ripe Rampager offers early access to the Screamroot loot, which unlocks the Potion Crate at the Bazaar once three have been sold. It also accesses the Ame-no-Murakumo, but this requires other loot items not available until later.
The player must defeat all Cactites in the area and look in the southwestern cul-de-sac of the Yardang Labyrinth. The cul-de-sac is just right of the exit to the Outpost.
The player should fight the Cactite in the southwest, near the Outpost, first, then move toward the inner passageways of the Yardang Labyrinth and defeat the two Cactoids that appear only when approached. If the player has moved far enough from the first Cactite's location, it should respawn along with Ripe Rampager.
Each Cactite/Cactoid killed has a 33% chance of spawning the Ripe Rampager. An easy way to trigger it is to save at the nearby Nalbina Fortress, kill all 3 in Yardang and reset if the Rampager fails to spawn.