BioShock 2

Though you yourself are a Big Daddy, killing a Big Daddy is still no picnic. In fact it's about just as hard as before. sheesh

You'll find the little sister and big daddy pair in the El Dorado, entrance on the second floor of Ryan Amusements. Though Sinclair says the Big Daddy won't attack you until he's attacked himself, he still gets spooked, so I'd say it's no guarantee. Keep your distance.

There's a heal station and a Circus of Values machine. Hack both for loot and also collect the ammo, First Aid Kit, and Eve Hypo lying around.

There's a chance of sneak attacking the Big Daddy at one location. There will be an oil drum that you can blast from cover that will ignite an oil puddle next to it. The Big Daddy won't see you so when he gets burned he'd rush around blindly looking for you before moving on. But that's only a fraction of his life bar accounted for.

The rest...

There's a big pool in the middle of the El Dorado, presumably an elaborate fountain fixture. Every time you attack the Big Daddy make sure you're between him and the pool with some eve in stock. Electro Bolt the pool as he charges you and he'll be stopped in his tracks for a few precious seconds. You can then hit him with gunfire (rivets seem to work best) and run away to repeat the process.

There's another pool along the floor in front of the bar. You can retreat and lead him there too (he initially stays around the main pool so you wouldn't get him there at the start).

Keep leading him on this shocking runaround and eventually he'll collapse.

Walk over to the weeping little sister and she'll perk up, holding her hand out to you. Adopt her at the prompt and you'll see this achievement pop up and gain a new companion! Congrats!

For those curious, the little sister is really on your shoulder! She'll make comments on some of your actions as you go. And if you stand against a large light, your shadow shows her perched smartly, ready for action. ;) You go, girl. ;p

Story-based achievement - You will come to a part in the story where you have to find a little sister, in order to get the little sister you must kill a Big Daddy, once you have killed the big daddy, walk up to the little sister and press the 'X' key, achievement will unlock after she climbs onto your shoulder.

Story related but you will have to kill a Big Daddy first and adopt 'his' little sister once he's dead (by pressing 'X').

You will face your 1st Big Daddy on Level 3 'Ryan Amusements'.

Be prepared because it won't be an easy fight (unless you're playing on easy). The Big Daddy will be in a room, alone with the little sister (there will be no more enemies in this room), make sure you explore the room first and get medkits, ammo, etc. There is a vending machine and a healing station in the room. The Big Daddy will not attack you unless you fire the first shot so when you feel that you're ready go for it. But once you shoot at him he will be relentless.

Unmissable storyline achievement. You'll get this in Ryan amusements, after killing your first Big Daddy. Follow the arrows.

For killing the big Daddy, don't bother with traps. Get close to him, and switch between shocking him and drilling. If you die, you'll respawn just outside the bar. Get back in there quickly, and his health won't regenerate.