If you've made it this far into Bloodborne, you shouldn't have too much trouble taking down the game's real final boss, the Moon Presence. Its attacks are fairly easy to dodge, and it gives you a huge window of opportunity to attack it when it activates its health-draining attack. Make sure to capitalize on that window as much as possible — that attack brings your health to zero, so you'll need to use the Regain system to get some of it back.
Check out the video above to watch us take down Moon Presence, and give it a shot yourself; if you can do it, congrats! You just finished the hell out of Bloodborne.