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Cyberball
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 +10% Damage will deal 27.5 damage on a Cyberball trigger (25 base + 2.5).
Scaling
Each Cyberball provides an additional flat 15% chance for the effect to be triggered, as well as an additional 25% of the player's Luck stat as damage. It takes 7 Cyberballs to guarantee the trigger, at which point each trigger deals 175% of Luck. This high flat damage scaling makes the Cyberball a very valuable item for any run with a decent Luck stat.
Item
Cyberball is an in-game item that can be bought from a Shop or can be found in a Crate. Most Items modify the Stats of the player, and some of them provide additional effects.