Slimes can get temporarily bigger if they drink huge amount of water but their movement is gonna be sluggish and slow due to their mucus being diluted. They also will be heavier and unstable, more mass but the same amount of zooids in the slime.

very intimidating slime person in dirty and full of scratches armor, oozing from the chainmail and wielding a huge sword. but once they take off their armor its just... blobby. blobby slime, maybe they still got the general shape of the armor but still gloopy and slippery. melty. slorp.