Yes, after killing Bibby Bloodbath for the first time, the player will get an achievement.
Apart from that, this boss is also part of the bosstiary, requiring 60 kills to complete it (Category Archfoe).
What is curious about this boss is that its cooldown is 24hrs instead of the usual 20hrs of archfoe bosses, and if you try entering the stairs before this cooldown is off, your timer will be reset back to 24hrs. This usually happens when the world change happens 2 days or more in a row on a server.
Also, this is the only archfoe boss so far that has a proper cooldown and doesn't have a cooldown hourglass in its tracker to help you keep track of this 24hrs. So the best way is to either check your "boss killed" screenshot if you have this option enabled, keep track manually down to the minute/second or just skip the world change in case you had it done the day before.
