This achievement is only achievable during the Halloween Event (2021: Oct. 15 - Nov. 16). There is a flying pumpkin vendor near the fountain on the Plaza who runs a Halloween-themed cosmetics Ghoulcery shop, where everything is purchasable via Ghoul Coins. This is not a technically difficult achievement, but it is a hard timegate.
Ghoul Coins are doled out during the Halloween Event for any number of in-game activities. Some examples are:
- Game Worlds (Minigolf, Ball Race, Little Crusaders, Zombie Massacre, Virus, Accelerate)
- Plaza Activities (Arcade, Casino, Bowling, Typing Derby, Laser Tag)
- Halloween Plaza Events (Ghost Hunting, Pumpkin Shoot, Mysterious Remains, Trick or Treat!, Halloween Character Visit)
As of Nov. 2021, you will have to purchase Ghoulcery items dating back to 2017, 2018, 2019 & 2020 worth a whopping 1,113 Ghoul Coins. Assuming a constant rate of Ghoul Coin generation of 1 Ghoul Coin per 4 minutes, that's around 74.2 hours of grinding (rate of 15/hr.) for this one achievement. You'll be here a while.
TU Devs have made enough activities eligible for GC so that you can easily combine some of the grindier achievements alongside this one. I recommend taking advantage of the monotony to work on mastery achievements for the various game worlds. Personal suggestions include:
- Ball Race "Conquered" achievements require 30 completions per map.
- Minigolf "Regular" achievements require 10 completions per map.
- Accelerate "Mastered" achievements require 20 completions per map.
- Virus "Survive" achievements require 25 completions per map.
- Zombie Massacre "Mastered" achievements require 10 completions per map and the "Dawn of the Dead" achievement requires 500 days survived.
Aside from that, I would also advise working through Arcade achievements if you're looking for more variety. All of them are some level of grindy (albeit less so than the Game Worlds ones) and get you tickets at the same time, and you're doing a lot of different activities as opposed to pressing W on Summit for 10 hours.
Good luck!