From Brotato Wiki
+2 % Damage for every 1 % Life Steal you have
You take 1 damage per second (does not give invulnerability time)
Item
Bloody Hand 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.
Unique
Bloody Hand is a unique item. Only 1 of each unique item can be equipped, and it will then no longer be offered in the Shop, and no longer drop from loot crates.
Bloody Hand
Bloody Hand Provides a large amount of Life Steal and Damage at the cost of dealing 1 damage to you each second.
Strategy
The self-damage of Bloody Hand triggers on-hit effects of characters such as Bull and Masochist; this can be strong synergy.
The self-damage will usually kill you if you hold a Weird Ghost which puts your current HP to 1 at the beginning of the wave.
The effect from Tardigrade is wasted by the self-harm.
Triangle of Power is completely antagonistic with the self-harm.