As Forza Horizon 4 is being delisted on December 12th, 2024, and the final Series (77) started on July 25th, 2024, if you started to play anytime after July 28th, 2024 then this achievement is deemed impossible to complete.
According to guides, you need the following done in the series:
- All Seasonal Championships (12 total)
- All FORZATHON Weeklies (4 total)
- All Seasonal PR Stunts (12 total)
- All 49 FORZATHON Dailies - These expire 3 days after they appear. (on FH5 you get the full week to do them, which is a lot better) Should you take a break like I did (I did do this back in 2018 when FH4 was Microsoft Store only, sadly) then you are out of luck :(
- All Trial Challenges (4 total) - These are RNG dependent on your teammates, good luck.
- All Playground Event Challenges (4 total) - Previously it required you to win the Best of 5 tournament, but now it is just to finish the full event. This was also implemented in Forza Horizon 5.
- 1 Monthly Rivals Event - You will likely win your rival as long as you do not bump walls (the Dirty Time penalty). This can be done any of the 4 weeks.
- 1 Monthly Ranked Match - You must reach Tier III (3) in Unranked Any Adventure online to qualify, then receive a rank. This can be done any of the 4 weeks.