Effects are special event animations obtained through the shop, triggered by the events that their type describe (for example, when you evolve, if you have acquired an evolution effect, the selected one from that group will trigger). They temporarily increase your vision against darkness (except dust). They can only be bought with an account.
The effect prices are shown below.
Kill Effects
Dust: 150 gems
Exploding Skull: 800 gems
Evolution Effects
Fireworks: 200 gems
Double Fireworks: 300 gems
Stars: 300 gems