Their powers were so creative, too!
And I liked the dance that the dad had to do fir every attack.
Also, did you notice how all the villains who discover the secret identity of Pantsu-chan keep it a secret? I think they're building towards something...

OOOOOH!!!! Sounds like you have a theory I'd love to hear. It's either a story element or the original manga-ka has something up their sleeve (cause you're totally right!)

There's not enough information to go on yet, but it is suspicious that every villain who discovers Pantsu-chan's secret goes ahead and keeps it a secret, even when their explanations sound fairly flimsy, like Plankton's excuse.
(Yes, I know that there is no confirmation that the shadowy figure who watched Pantsu-chan transform was secretly Strangulu, but the music they played was super ominous, and the forum argument was fairly convincing.)
I think that it isn't Pantsu-chan that they're protecting.
Look, early in the season it was hinted that Pantsu-chan has more than one transformation, so my current theory is that the villains are trying to prevent a transformation into a more powerful and potentially dangerous mode by keeping Pantsu-chan pacified, as it were.

They knew way too much, secrets that were only known to Pantsu-chan (obviously), Plankton, and in the one case, Mr. Krabs (thanks to Mecha-Krabs!) It all points to there being a chessmaster behind the scenes. Remember when Janiko asked Martizu if they should use "the Whale Horn"? (YES, I CAPITALIZE IT.) I know most people will shout me down as it being just a quirk of translation, since we never found out what it was, but I bet there's going to be another villain with a Whale Horn that they got from the chessmaster!