The BTs featured in Death Stranding are some of the most unique in any video game, and that's not just because the main character, Sam Bridges (as portrayed by Norman Reedus), needs a baby strapped to his chest in order to detect them. These invisible monsters bring about rain called Timefall that rapidly ages anything it touches, and anyone that gets too close to one is sure to meet certain doom. At least, that's the case for anyone who isn't Sam.
The lead protagonist in Death Stranding is capable of repelling these monsters known as BTs (Beached Things) with various fluids from his body. This includes blood, urine, and poop, all of which can be fashioned into handy-dandy grenades. While bizarre, it's actually possible to defeat Death Stranding's most terrifying monsters with the various bodily excretions-turned-armaments. Of course, this is easier said than done.
In the early portions of the games, players will be left without a means of directly combating the BTs; instead, they're forced to navigate around them. This is terrifying, but after avoiding the BTs players will eventually be able to take them on and put them out of commission. This is done by crafting grenades at settlements that feature 3D printers. The materials required aren't too extravagant, and filling up on 1 and 2 Grenades is as easy as utilizing the toilet in Sam's Private Quarters. Yes, players can even pee on BTs to make them go away if they want.
The most effective item, however, is the Hematic Grenade. They're unlocked pretty early on and will do massive damage to BTs. Other weaponry is unlocked as players progress through the story. These include bullets made from Sam's blood and several other anti-BT accessories. With something like a Hematic Grenade, however, it's a matter of managing Sam's energy levels during use. Exhausting him will leave him open to plenty of unsavory attacks from a BT – most of which involve a Game Over screen.
As mentioned, the first indication that there's a BT in the area comes from rain. If there's rain then there's one nearby, so it's important to remain diligent in these times. Truth be told, it's better to just avoid the BTs if possible, as they can do a lot of damage to Sam's equipment. Some of them are quite tough as well, but if push comes to shove and the entire ground turns to oil, those Hematic Grenades will prove most useful. Just be sure to comfort BB after the encounter is over.