The King Amoeboid was a large Amoeboid that lived in the sewers on planet Aquatos. Each of them carried a Sewer Crystal which could be collected by defeating it. There were two kinds of King Amoeboids as well. One was found by approaching massive green walls. The other kind could be found in the secret section of the sewers (that could only be accessed with the Gravity Boots) by approaching sewer grates. It was very hard to discern if you had defeated them or not, so you had to check your map if you had the Map-O-Matic to find yourself and to see if there was a Sewer Crystal there. If there was one, you had to use a powerful weapon to attack them. This mutated kind had double attack powers, but half the health of the normal kinds of Amoeboids.
In Secret Agent Clank, they appeared in Prison and had a crown on their heads, probably denoting their 'King' status.
A simple way to kill a King Amoeboid was with a shot from the Nitro Eruptor or a charged up blast from the Shock Cannon.