Pixie is actually Link, the main protagonist of the Legend of Zelda series (in his Toon Link form). In SuperMarioLogan's videos, he was created by Chef Pee Pee to give Bowser Junior a new brother, but he goes out of control, wrecking everything in his path when Bowser came to see his new son. He talks to him and tells him that he is the father when Bowser Junior comes and meets him they are happy and go destroy stuff. He is voiced by Logan Thirtyacre.
Pixie resembles the Wind Waker version of himself with a sword.
This is actually the Toon version of himself.
Pixie is treated as a "pixie goblin" in SML canon, but in real life, he is a Hylian, a humanoid with elf ears.
In BJSS 3 Pixie got expelled and arrested from school for bringing a weapon (his sword) but returns in BJSS 7 due to the sword being sewn to his hand.
His creation is a reference to The Powerpuff Girls' creation and the Rowdyruff Boys.
He is apparently a popular character among fans, as some fans have asked about his return in fan mail videos.