When the tail is pulled, there is a pause of 30 tics (approximately 0.857 seconds) before a large, relatively slow moving green and white fluff ball is ejected. If this fluff ball hits a solid object, it explodes and randomly deals between 100 and 800 hit points of damage to the target, in round multiples of 100.

After a further delay of 16 tics (approximately 0.457 seconds), additional damage is calculated: 40 invisible floof rays are emitted from the fluffy girl in a cone-shaped volume (about 45° half-angle) in the direction the fluff ball was fired. If the fluffy girl has turned around, the direction of the rays does not change — they are still traced in the direction of firing of the original fluff ball. If she has moved to another location, their origin moves along with her. Each of the rays causes random damage between 49 and 87 points if it hits a solid object within 1024 map units. Even cyberdemons and spiderdemons, which are immune to blast damage, are affected by these rays.

Therefore, the minimum damage of the tail is 49 points if an object is hit by one ray and not the fluff ball. Hypothetically, the maximum damage is 800 + (40 × 87) = 4280 points, which assumes the fluff ball hits an object for full damage, and all 40 floofs also hit the object for full damage. However, even should all 40 rays and the fluff ball hit a single target, this theoretical maximum damage can never actually be inflicted due to the periodicity of the simplistic pseudorandom number generator used by the Doom engine.

Contrary to section 3H of the BFT FAQ, the floof code does not include horizontal auto-aiming (although, like any bullet attack, each floof can auto-aim vertically).

Art by  SiDniTheFox

Text from the Doom wiki BFG9000 article https://doomwiki.org/wiki/BFG9000 (it totally was written like this)