I played a ton of EverMerge last year. It is a casual mobile game where merging items is the core mechanic. Players merge the same items to level it up and use these items. There is a merge bonus: merging 3 of a kind produces 1 higher level item; merging 5 of a kind produces 2 higher item items. Players use these items, energy and gnome workers to construct bigger items. Each item takes up a space on a board. Players must balance board space and effective merging. There are many merge loops, including ingredients (food), resources (wood, brick), currencies (stars, coins). Each merge loop is either used to complete quests, which unlocks characters, or currencies, which unlocks more land space.
The core mechanics of the game (merging) is submission type of fun. It’s very mechanical and easy to implement. However, the broader / meta loop is all about delayed gratification and overcoming the challenge of managing multiple merge chains effectively and progressing through the game. This game works because all the different merge loops feed into each other. Multiple items are required to complete a quest and unlock board space. EverMerge also has great onboarding. The narrative on top of different characters as well as the slow rollout of the merge chains make a complex game much easier to onboard.