When the fight against the Abyss Watchers begins, it seems like a simple battle against a slightly tougher enemy. The Watcher will attack you with a greatsword, and this can be easily dealt with by either blocking with a shield, or rolling. His moves are fairly easy to read. He has a string of 5-hit combos, so be sure to wait them out before going in for your attack. He doesn’t have a lot of poise either, so your attacks will stagger him pretty easily.
As you wear down his health, other Abyss Watchers will start waking from the dead, one by one. Here’s where the fight gets a little tricky. When the first clone spawns, both the boss and the clone will target you. I suggest dodging their attacks and waiting for the second clone to spawn. Once the second one spawns, the second clone will either fight the first clone or the boss himself. If he engages the boss, take this opportunity to finish off the first clone. If he engages the first clone, those two will likely finish each other off, so you can focus on the boss as per normal. It’s also good to note that you can backstab the Abyss Watcher. If the boss ever gets distracted by the other clones, this will give you openings for some backstabs. Do take note that clones will continuously spawn during this phase of the fight.