From Brotato Wiki
Blood Donation
Item
Tier 3
Stats
+40 Harvesting
You take 1 damage per second (does not give invulnerability time)
You take 1 damage per second (does not give invulnerability time)
Price
50
Item
Blood Donation 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.
Effect
Blood Donation provides a large amount of Harvesting for its price, but comes at the cost of dealing 1 damage to you per second. The effect can easily kill you over the duration of a wave if you don't have sufficient healing to counteract the damage.
The Self-Damage of Blood Donation triggers on hit effects of characters such as Bull and Masochist, providing a powerful synergy. But it also leads to terrible results if combined with Weird Ghost or Triangle of Power