trying to find an old cartoon

i’m trying to find an old cartoon i used to watch! so basically the plot was under the sea, and there was a princess (i think) living there. then there villains were little yellow monsters that were rules by one big yellow monster, he basically lived and walked around in something similar to what sandy from spongebob had on her head, but he was completely covered by it. i also remember it had kind of a purple vibe if you know what i mean. pls help me!!!