Keep on damaging him untill he turns dark purple. Make sure to have the Sponge Thing Sticker with you! When he turns dark purple use your sponge sticker ONLY! At this point, when he attacks, the sponge will absorb the poison and throw it back at him.
Additionally, how do I get the last wiggler segment?
Your search for the fourth and last Wiggler segment begins on an area with three floors of bushes. Upon walking, you notice a Blooper peaking out of the first level. Walk behind the bush and jump over the poison puddle. Once you get close enough, two Bloopers will surface carrying the last Wiggler segment.
In this way, what do you get for completing the sticker museum?
There are 64 Thing Stickers and 96 Battle Stickers total, and completing each section unveils a new exhibit. Completing the Battle Stickers section unlocks an enemy gallery with enemy attack patterns, and completing the Thing Sticker section unlocks a music gallery.