From Brotato Wiki
Cyberball is an in-game item that can be bought from Shop or can be found in a Crate. Most Items increase the Stats of the player while some of them provide unique effects.
Cyberball's damage is a direct effect, does not crit, lifesteal, nor do "normal" attack things.
Similarly to the Baby Elephant, the Cyberball's damage dealt is affected by the player's Damage stat -- so a player with 100 Luck and +20% Damage will deal 30 damage on a Cyberball trigger (25 base + 5).
If you have more than one, each Cyberball will trigger independantly each time you kill an enemy.
So for example if you have 3 Cyberballs and kill an enemy, another enemy is chosen, and then the game rolls a 100 sided die three times. For each succesful roll, the target takes damage. So with 3 Cyberballs that deal 10 damage on hit, the target could take 0, 10, 20, or 30 damage.