"Okay, about three years ago my egg was found by an older yoshi. I was put up for adoption before I hatched and my egg was taken by *****. He raised me in the ways of evil, to serve the King. For about a year, I was a faithful knight. ***** gave me his trusted sword, Little Excalibur to fight with. In an effort to be more powerful, I started adding to Li'l X's power. I stole swords from across dimensions to add to her. Eventually, I stole Ultima Weapon from Cloud Strife and molded it with her. After that, she became Ultima X. I fought in many battles for the King and his sons. However, I started to get bored with the whole "evil" thing. The King kept saying how he wanted power, but according to what ***** taught me, money IS power. So I stopped being so power hungry and became money driven. I decided to use the two main things I had learned in life when job hunting: fighting and kidnapping. I became a bounty hunter. I got many jobs over the past two years and accepted many kinds of currency: gella, gil, gold coins, frog coins, golds, etc. One day, not too long ago, King Bowser came back to talk to me, without ***** knowing. I was asked to capture the Super Smash Stadium fighters. He agreed to pay me 500 frog coins and a slew of items for each fighter I captured. He said that he would easily be able to sell Link to Ganondorf, Samus to Mother Brain, Pikachu to Team Rocket, and the other fighters to other people. I accepted his offer and walked toward Yo'ster island to get in touch with an old childhood friend: Boshi. He's a few months older than me, and that's actually a lot. I'm three in human years, but about 18 in yoshi years. That's 6 yoshi years to one human year. Anyway, we started capturing fighters left and right, and eventually all that was left was Mario. Bowser told me to leave Mario to him, so I agreed. We went back to the castle to receive my pay. When he got there, he gave me the money, and offered us another 500 frog coins if we would help guard his castle in case Mario brought friend: we agreed. Mario and Mega Man showed up on the roof to battle us. Boshi and I seemed to be winning that match, but Mega Man took out a stinky trout. I don't know about you, but to me, something smelled fishy. Anyway, after the fighters were back, I explained to VGW, Pat, Lemmy, Lugia, and the others that I'm not evil, I was just doing my job. They accepted that and I asked if I could join the SSS. I had enough frog coins to be set for a long time. After many, MANY discussions, they agreed to let me join. And that brings me to today."
Of course, since that time, Killer has experienced utter decimation against Roy in Season 3 and left the Stadium to train. Some say he is searching for Sephiroth to obtain Sir Tomintul's Hyper Sword and Sephiroth's own Masamune and merge them with his own sword. However, most say that he will appear only when he is needed. Needless to say, Killer will always be a fan favorite of SSS.