Mother Brain is an enemy in Bloodborne that will frenzy and kill you if you go anywhere near it. The bad part is there’s a Blood Rock near it which you can use to get any weapon to +10.
It is really easy to kill it though and get the Blood Rock and the video below shows what exactly you need to do. There’s only 1 Blood Rock available in each playthrough so it would be wise not to miss it.
You can also get a Moon rune which gives 30% Blood Echoes from enemies after you do the ‘Make Contact’ gesture for 30-40 seconds.
Once you get a weapon to +10 you will get the weapon master trophy as well.
Check out the video below.