Sonic the Fighters

Start Arcade mode set difficulty to easy. attack power to 3, rounds to 2, and barriers to 1. Move cursor to Amy press start and then press A and you will choose character Honey the Cat. Start round by pressing RB this is a lon range attack and will normally pin your opponent close to the outside of the ring now spam Y,Y,Y and this should do a 3 hit combo knocking your opponent to the ground on the 3rd hit. Continue the Y,Y,Y attack till you win. At the end of the match "Bleep-Bloop" 20 GS easy as pie.

For this achievement you'll need to complete Stage 1 of Arcade Mode.

For the Arcade Mode of Stage 1 you'll be facing against Knuckles the Echidna. If you want an easy going match you can choose Easy mode, with attack power +3, and only 1 barrier so you can easily overpower your opponent for an easy win.

Once you've defeated Knuckles you'll earn this 20G achievement.

The following video will depict this solution.