The Darklings are creatures that look similar to their master, Dimentio. They are loyal to Dimentio.
After the Purity Heart destroyed the Chaos Heart, Mario and Friends thought that Dimentio was gone for good. However, he left behind an immortal shadow of his power. Mario and Co. didn't know that, so they thought that Dimentio was dead. However, he wasn't. He used the tiny bits of what was left of the Chaos Heart to create Inkhearts (yes, yes, I know there's a book called inkheart). He had 8 Inkhearts, and he used them to create servants of his own, called Darklings. That was the beginning of the Darklings.
When Vex was created, he was made at the age of 17. Vex is quite a trickster-he loves putting people in puzzles. He is the oldest Darkling and the Darkling with the highest rank.
The slightly green glow around his head is from his powerful aura.
"Magic is overrated" is the famous quote by Quantum. He is 15 years old (according to the Darkling Prognosticus). He loves science and doesn't like his brothers because of their magic.
Ion says, "You say I look like a bee?! Well, watch as the power goes out in your house!" Ion is 14 and has a very short temper. He has powers over electricity and is working with his close brother Quantum to build a time machine.