The Mega-Slayer was built by Alistair Smythe.
Tablet of Time
When the Tablet of Time was brought to Empire State University, Kingpin learned of this and had Smythe send the Mega-Slayer to steal it. As the Mega-Slayer arrived at ESU it burst into the Neogenics lab. At that moment Spider-Man was there and knew that the Mega-Slayer was after the Tablet of Time. As Spider-Man grabbed the Tablet of Time he web swung into New York City and the Mega-Slayer flew after him with jets in his feet. As the Mega-Slayer was captured by the Mega-Slayer it almost killed Spider-Man. However, Kingpin ordered Smythe to have the Mega-Slayer return to their base with the Tablet of Time.
Now that Kingpin had the Tablet of Time he discovered he also needed Curt Connors to translate the ancient writing to figure out how to use it. Smythe then sent the Mega-Slayer to Curt Connors house to abduct him. However, at that moment Spider-Man was there. As the Mega-Slayer burst into Curt's home he was easily able to take down Spider-Man. The fight then led into the street where the Mega-Slayer was attacked by Curt Connors who had transformed into the Lizard. The Lizard then went into the sewer. Smythe was unable to find Curt so he instead had the Mega-Slayer capture Margaret Connors and told Spider-Man to meet him on top of the Empire State Building with Connors if he wanted Margaret returned alive.
A few hours later the Mega-Slayer arrived on the top of the Empire State Building. Smythe saw that Spider-Man did not have Curt Connors and attacked him. The Mega-Slayer chased down Spider-Man and was ready to kill him. However, Smythe received a video message from Kingpin who told him that he had set up a meeting with Silvermane to exchange the Tablet of Time for his wife, Vanessa and Smythe had the Mega-Slayer leave without killing Spider-Man.
The Mega-Slayer shortly arrived at the meeting site and he gave the Tablet of Time and Alisa Silvermane to Tombstone in exchange for Vanessa Fisk. However, Smythe double-crossed Tombstone and captured Vanessa, Alisa, and the Tablet of Time. Tombstone expected a double-cross and had one of his men shoot the Mega-Slayer with an RPG which damaged it. Spider-Man intervened and was able to stop the Mega-Slayer from getting the Tablet of Time. The Mega-Slayer then returned to Crime Central to be repaired.
Silvermane then stole the Tablet of Time and was able to capture Spider-Man. As Silvermane prepared to use the Tablet of Time to make himself young the Mega-Slayer arrived and attempted to kill Silvermane. Tombstone then tackled the Mega-Slayer and was able to damage it. The Mega-Slayer was too badly damaged and all Smythe and Kingpin could do was watch events unfold through the Mega-Slayer's view camera.
The Mega-Slayer's enhanced size gave it super strength.
The Mega-Slayer's surface was so slick that not even Spider-Man could stick to it.
The Mega-Slayer had jets on its feet which allowed it to fly.
Missiles could be launched from the Mega-Slayer's wrist.
The finger tips on the Mega-Slayer could fire a laser or a pulse blast. The pulse blast could be used to send enemies flying across the room.
The Mega-Slayer could also shoot grapple hooks from its wrist to capture enemies.
In the comics
The Mega-Slayer was the mark 14 spider slayer.
The Mega-Slayer was built by a man named Max Young, under the command of Alistair Smythe.
The Mega-Slayer had three faces, each of which represented a personality of Max Young, who had severe multiple personality disorder.
It found Spider-Man at a prison where he was investigating, and attacked Spider-Man and Black Cat. The Mega-Slayer was winning until Spider-Man tricked the three personalities into arguing with each other. Eventually the Mega-Slayer destroyed itself.