Heavy Metal Bloon

The  (also known as Robotic Lead Monstrosity or Underground Boss) is the final boss of Bloons Super Monkey 2 that appears in Mount Magma. It is a giant rocket-propelled metal blimp shaped like a Lead Bloon. Not only is this boss extremely difficult to pop/destroy, but it also defends itself by creating weapons and barriers out of Shielded and Phasing Bloons.

Trivia

 * Despite looking like a Lead Bloon, the Heavy Metal Bloon can be damaged by darts, boomerangs and their upgrades.
 * It has what looks like an extremely electrically charged Shielded Bloon, that seems to be powering/controlling the boss.
 * It has roughly 16,000 healthpoints.