I kinda wish My Goldfish Is Evil came out later then it did, because there is a lot of potential for a number of cool plotlines that never got to become more developed and fully unleash their potential:
In the season 1 finale "Icing on the Cake!", the show finally reveals a lot about Beanie's dad: his plane crashed and neither the plane nor any of the passangers were found; before getting on the plane, Beanie's dad gave him a birthday present - Admiral Bubbles.
The opening of season 2 is different from season 1: now, we are shown the said scene of the dad giving Admiral Bubbles to Beanie before his flight.
To add fuel to the fire, in the third episode of season 2, when Admiral Bubbles wants to use Ouija board for another one of his evil plans and looks through types of ghosts he can summon, the very first one he names is missing relatives.
Unfortunately, it was the last time the theme of the missing dad was brought up.
Admiral Bubbles's background
The details of Admiral Bubbles's history are sprinkled throughout the show - from great martial skills that must have taken years to perfect (his overpowers much larger opponents on many occations) to partnerships with shady people.
But what caught my attention the most and might be directly tied to Admiral Bubbles's desire to inslave the human race is him being a research subjects at one point in his life.
Even though Admiral Bubbles still can be sympathized with at times because his hatered of humans is understandable, I still think he deserved a proper exploration and a backstory that would show how he became the villain he is.
There's an episode where a new character Mr. E, the owner of the local pet shop, shows every sign of being an alien (has a strange device on his neck that seems to be a translator and constantly messes up words because it glitches, has a secret lab, has a photo with a UFO in the background and is scared of the organization that supposedly fights aliens) but he desperately tries to not blow his cover.
However, Mr. E's plotline doesn't really have any conclusion and the character doesn't have any other appearances.
But, as we know, if canon can't give you what you want, do it yourself. So, I'm likely to do some stuff on the abovementioned themes.