Why is Yin so interested in bad boys and is also able to become evil twice? Yin is the sign of darkness of the Yin and Yang symbol (in other words, the black half) so it makes sense why she's naturally like this.
Why is Yang's sword made of bamboo? Master Yo probably made it and pandas do tend to eat bamboo so...
Bonus points in which Master Yo was shown to chew on Yang's sword occasionally.
The writers were fairly accurate in incorporating the aspects of Taoism into Yin and Yang's personalities; also, Yin and Yang's ear shape are much like the Taoism when put together.
Yin, whose color scheme is pink and purple, has blue eyes. Yang, who is blue, has purple eyes. Much like the traditional yin-yang circle—with a white circle in the black half and a black circle in the white half— the two have each other's color in "dots" on their bodies.
Herman, the ant, having super strength may just seem to be there to make him a foil to his brother, Carl, the wimpy wizard. However, it can also be noted that ants have the strength to life about 5,000 times their own body weight.
In addition to making him an opposite to his magic-using brother, Carl, his brother's ability to seemingly survive a LOT of punishment may be referencing real life cockroaches' super-survival skills.
There's a subtle hint to the reveal of Master Yo being Yin and Yang's biological father. Both Yo and Yang have purple eyes, and Yin, while not having purple eyes, wears a purple bow of the same shade.
Why are Carl and Herman so powerful when they combine their strengths? The very simple concept in the show's opening. "When might and magic work as one". Their only issue is that they almost never work as one. Since they're so busy arguing and fighting, they can never win.
In "Disap-Eared", Yang becomes invisible but he messes up the spell to the point that nobody can see, hear, or even touch him; in addition, he's also able to walk through almost anything. It may not seem that creepy at first until you consider that Yang could have been intangible forever which isn't the most lighthearted of fates.