The blog it was created on was an ARG, or alternate reality game, which is an interactive networked narrative that uses the real world as a platform and employs transmedia storytelling to deliver a story that may be altered by players' ideas or actions. The "players", in this sense, are the followers of the account, and the general end goal of the original storyline of the account was to bust Sanzy, along with possibly Fundyne, out of the laboratory, though the 2017 revamp is unclear.
AU Plot Summary
The being known as "Sanzy Fresh", and subsequently every other fresh, was created due to a simple mistake of trusting a stranger. The doctor M.C. Radster would simply persuade the optimal subject into following him to the laboratory, in which he'd assimilate and trap them inside the testing program. His game was cruel.
Radster had a secret goal: to infect every timeline with a virus of his own creation. He was once an average Gaster, but once he drove himself mad after falling into the core, he vowed revenge on all that forgot him. He started by formulating a serum, one that would dull the senses and personality of those carrying it in their body, as well as increase their suggestion. He could bend anyone to his will, as long as it worked.
He went back to his own timeline to test it on two he knew best- his own child sons, Sans and Papyrus. They died in the process, and caused Radster to rethink his methods.
Timeline hopping was too big of a hassle for him. He needed something easier.
He moved to a dead timeline, one that had been emptied of people long ago, and set up shop in the Hotland laboratory. The virus was perfected, though it had an odd after effect.
It caused the infected subject to act like they were from the 90s. Not the most helpful side effect, but it was unavoidable at this point.
He set to testing there, kidnapping subjects from alternate timelines to house in his laboratory using a portal he'd built with his own two hands. He infected a Papryus first, reprogramming his fragile, hurt mind once he'd been converted to follow his orders and treat him like he was a father figure. He'd be more willing to listen that way, after all. He was Radpyrus now.
Radster only hoped future subjects would be the same.
Fast-forward to the present, with the proposition of a timeline reset for a genocide run-stricken Sans. He'd do anything to get his brother back. He couldn't keep looping like this- he needed him back. He accepted the offer and followed Radster into the portal he had emerged from.
Radster was obviously lying, converting Sans just as he'd done to Radpyrus. He was now Sanzy Fresh, the 90's dude with a bodacious 'tude. After him came Fundyne, who held strongly against the lab's treatment at first, but began to cave.
Radster now had his pawns.
Time to display them to the internet.