Values change whenever a pet's demand or availability changes

Typically old pets gain value due to less availability caused by unobtainability combined with users logging off and never returning with their pets

Demand also changes, typically by social media influence, but also reoccurring trends like holidays and seasons

A pet can increase in value for two reasons. Either the demand of the pet increased, or the availability dropped.

Higher demand means more people want it and are willing to «pay» more. When people are willing to «pay» more, the value increases

Lower availability means fewer people are offering a pet. This makes the pet harder to get, you need to «pay» more and the value increases

A pet can decrease in value for two reasons. Either the demand of the pet dropped, or the availability increased

Lower demand means less people want it and are willing to «pay» less. When people aren't willing to pay as much as before, the value decreases

Higher availability means more people are offering a pet. This makes the pet easier to get, you can «pay» less for the pet and the value decreases