Amplified Amplifier

The Amplified Amplifier is a treasure found both in Pikmin 2 and Pikmin 4. It is actually a. In Pikmin 2, it is found on the Shower Room's seventh and final sublevel. Collecting it prompts the Hocotate ship to create a piece of gear, the Mega Tweeter, which considerably increases the range of the leaders' whistles. In Pikmin 4, a redesigned Amplified Amplifier is found in the Below-Grade Discotheque's fifth and final sublevel. Unlike Pikmin 2, collecting it does not unlock any upgrade.

Collecting the treasure in Pikmin 2
The Amplified Amplifier is held by the boss of the cave, the Ranging Bloyster, so a battle is required to retrieve it. Like some other treasures, if the player defeats the Ranging Bloyster, but does not have enough Pikmin to carry the Amplified Amplifier, which requires the strength of twenty Pikmin, it will change weight to match the player's army. Note that due to how sublevel generation works, it is possible for the Ranging Bloyster to not spawn, making it impossible to obtain this treasure, as detailed here and here.

Collecting the treasure in Pikmin 4
The Amplified Amplifier is inside the boss of the cave, the Groovy Long Legs.