Echo! was accidently created by Dream!Sans. While he was fighting Error, Dream accidently struck a branch on the tree of dreams and there was a very loud "Boom". No explosion, just the sound... and then there was Echo.
Echo! is a black skeleton wearing a white tuxedo and gloves, along with a pair of sunglasses. He looks more like a shorter Papyrus then a Sans. He wears a white fedora with a black band. Also, for some reason his teeth are white instead of black.
The kindest way I can describe Echo! is narcissitic, the most honest way would be "full of himself". Echo is made mostly out of Dreams of Fame, so he is obsessed with becoming famous.
Echo! has the ability to play any character theme song, and then use the characters powers (e.g. Megalovania lets Echo! use Gaster Blasters, bone attacks and gravity manipulation)
He has also created two fan songs to let him use Nightmare and Dreams powers.
Dream my Dream (Dream!Sans)
Your Best Nightmare (Nightmare!Sans)
He also has a Jazz trumpet he fires Sonic Booms from, or use to increase the positivity levels of a AU with his music.
Song of Destruction- Echo! plays a eerie tune on his trumpet, if he finishes the song he claims the entire AU will be destroyed, however this speculation since he's never actually finished the song, he is always attacked before he can.
Dream!Sans- While Dream! treats Echo like his son, Echo doesn't think of him as his father, insteading prefering to think he's the trees "upgraded model" of Dream.
Nightmare!Sans- Echo is either too brave or too stupid to be afraid of Nightmare!Sans
Ruby Emerald- Do not get him started. He finds her selfie obsession and god complex annoying
While Echo! is no currently dating anyone seriously, he does think he is irresistable to woman
"Money...Check, Good Looks...Check, Ability to give them literally anything they want...triple check, yep I'm irresitable"- Echo literally says this into a mirror every morning.
His font matches that of whatever character he is mimicing during his fight
His mother is technically the tree of dreams, Error is NOT related to him
Lives in his conjured up ETT resort.
His birthday is a reference to Micheal Jackson