Ok. This guide's purpose is to help you tear through Legacy Mode and get the 8 achievements involved worth a total of 315 gamerscore. I realize it isn't that hard to get this, but for those out there who are horrible at the drills like me, this is a much easier way to do it without having to do the drills that much.
Everyone knows the basic goals that need to be achieved to reach the rank of GOAT in Legacy mode:
-- Win percentage higher than 90%
-- Popularity higher than 95%
-- Number of fights exceeds 50 (meaning you must compete in 51 total fights)
-- P4P rank exceeds 5
-- Defend title 8 times
-- Hold at least 3 titles
First create a new fighter in Legacy Mode. Make him a light heavyweight with max reach and max height. I made my boxer a power puncher and suggest the same for you. You should be going for first round KOs for the entire 51 fights. Customize the rest of your boxer as you chose.
Next, before you enter the amateur tourney, be sure to turn your legacy mode settings to the lowest difficulty and turn all the stats for your boxer up and all the opponents down, including strike frequency.
Be patient in the amateur tourney and just try and get more punches than your opponent. Its pretty easy to win. Winning this will get you 20.
Once you go pro, always pick the highest rank boxer. My first 10-15 fights I set my fights exactly 6 months apart to train 3 weeks before the fight. I would train right and left hand power on auto-sim, and manually do free sparing because its pretty easy to get champion on. Once you get your boxer's power to around 90 start auto-simming other stats and building them up. After about 15 fights start training only two weeks before a fight, and continue to mostly auto-sim your skills (except for free spar.) Eventually your boxer will max out with this formula at about 85-87. But that's good enough to KO dumb AI for 51 fights.
Be sure to move up a weight class after winning the title at LHW. Go to the body frequently with your power puncher, it opens up the head. You should be getting first round KOs.
Avoid Mike Tyson and Ali at HW unless they have a belt you need. They both have one punch KO potential no matter how bad the AI is.
If you win every fight up to 51 retire. Be sure it says you are The Greatest of All Time. If you do this, you should receive the following achievements along the way:
-- FROM CHUMP TO CHAMP (20): win the amateur tournament in legacy mode
-- UNDEFEATED (20): win 5 consecutive legacy mode fights
-- THE ROAD IS LONG (10): win 10 fights in legacy mode
-- THE CHAMP IS HERE (40): win a championship belt in a single weight class
-- MOVIN' ON UP (30): move up a weight class in legacy mode
-- THE LATEST AND GREATEST (50): retire as a superstar
-- BIG GLOVES TO FILL (65): retire as a hall of famer (unlocks achievement for retiring as a superstar if not earned)
-- GOAT (80): retire as the greatest of all time (unlocks achievement for retiring as a superstar and hall of famer if not earned)