Achievements in the game are missions that you can complete by playing with certain champion, playing in certain mode, using miracles and other.

Every time you complete an achievement, you will get 50 hearts and 100 gold.

Every 1000 hearts you can upgrade something in the MINImax antique shop.

You can read more about this here:

https://minimaxtinyverse.zendesk.com/hc/en-us/articles/360043093333-What-are-the-Achievements-for-