I’ve played a mobile game named ‘Merge Dragons!’ which my girlfriend introduced to me.
The objective of this game is to clean sky using dragons that has been polluted by bad things.
You should use your dragon to collect hearts from flowers to clean the sky.
You can upgrade a dragon using merge after having collected three same dragons. Then you can merge these dragons to next level dragon.
I believe this game is limitless because next level dragon needs three dragons from the previous level. For example, if you want to merge to 5 level dragon you need 3 dragons of level 4. level 4 dragon made by three 3 level dragons. one level 3 dragon need three level 2 dragon.
It means level 3 dragon needs 9 level 1 dragons. but I can collect only 1 dragon per day. It never ends.