Achievements has been the hygiene for user churn prevention since they've been introduced in games. Especially important if we move towards game weeks with lesser user engagement on the daily basis

Achievements can help us elevate 2 aspects of our platform:

Collectables. Sticker albums was a great start, but to gratify it with achievements will make it to another level

Fantasy consistency. Players are giving up sometimes on playing. They are bored, they forgot, whatever reason. Achievements helps them to keep pushing for a little more to the next goal. And if designed smartly, there is always another goal just around the corner.

In scope:

Achievements require beautiful popups notifications to share the progress (so user knows that he is almost there) as well as achievements received announcements for user

New page (or some extension of collection page) to view current ones

New separate service (and database) to track and announce the completion of those items

Optional:

A way to brag/highlight the achievements on user page

Display user level (based on achievements) together with avatar

Avatars (or maybe other cosmetics) as part of achievements rewards

What to track:

The feature should affect User Churn, length of the sessions and, potentially, packs/marketplace sales

Notes:

Physical prizes for some achievements would be an amazing extension (just a T-shirt or scorestars labeled merch). It drives the motivation up significantly