Eternal Sugar Cookie (Korean: 이터널슈가 쿠키[1], iteoneol-syuga kuki) is one of the five Beast Cookies of Cookie Run: Kingdom. They appear briefly in a Secrets of the Silver Kingdom update (v.5.0) cinematic, only being vaguely mentioned otherwise. Their name is stated only on the 3rd Anniversary of Cookie Run: Kingdom website.
Eternal Sugar Cookie wields the power of Sloth, a corrupted side of the Virtue of Happiness they once held. They were the original owner of 
Hollyberry Cookie's Soul Jam, being stripped of it upon their descent into villainy.
Trivia
- Eternal Sugar Cookie appears to correspond to the Forgotten Sugar Paradise/Sugar Paradise region of Beast-Yeast.
- The "Recruit Adventurers" subpage of the 3rd Anniversary of Cookie Run: Kingdom website, being published on January 5th, 2024 at around 2:00 pm GMT +9, accidentally included far more information on Beast-Yeast and the Faerie Kingdom than was intended. Here, Eternal Sugar Cookie, alongside
Silverbell Cookie, 
Mercurial Knight Cookie, 
Elder Faerie Cookie, and the other Beast Cookies, was revealed. This content was swiftly removed and reinstated on the site's main page about 4 days later with slight changes.
References
