Strategy against them

Always ensure that you have full Health, as well as a reliable supply of First Aid Kits, EVE and ammunition before fighting a Big Daddy, as these are one of the toughest enemies in the game.
It is recommended to study a Big Daddy's path and stalk them, so as to attack them where you have the biggest advantage. Study the environment as well, so as to be able to formulate a winning strategy.
Always ensure that you have complete control over the fighting area (i.e. the place is clear of Splicers and all Security Devices have been hacked). Loss of control might signify defeat in the later stages of a fight.
Never take on another enemy while dealing with a Big Daddy, except in some unique cases. If you are forced to fight another enemy, take it down first and come back to the Big Daddy.
Little Sisters always stop to drain ADAM from any nearby corpse they find. Corpses can also be moved by you, enabling you to choose where they want the Big Daddy they're targeting to halt.
Piling up several explosives onto a Big Daddy's path (preferably on top of an oil slick) and blowing it up at the right moment is a cheap and effective way of killing, or at least severely injuring, a Big Daddy. If the enemy survives, they will be on fire, which will drain their health continuously.

Recommended Plasmids

Hypnotize Big Daddy is, obviously, a prime choice when faced with a Big Daddy, as it turns the hulking creature into your bodyguard. It can also be used to pit two Big Daddies against each other, which is both an entertaining and effective way of killing them.
Enrage can be used in a similar fashion: by Enraging a Big Daddy, you can clear an entire room to a minimal cost in EVE. Make sure you takes your distance, as the Big Daddy may assault you if you are the closest to them.
Incinerate! is recommended against Big Daddies, as a single cast will drain a significant portion of their health over time.
Telekinesis may come in handy if there are explosives lying around. It can also help you formulate various different strategies.
Electro Bolt will temporarily stun the Big Daddy, as well as deal increased damage (especially in water). Do not attempt to One-Two Punch the Daddy unless you possess the correct Gene Tonics, though, as the Wrench deals only quarter damage against Big Daddies.
Insect Swarm will distract the Big Daddy as well as deal continuous damage, allowing you to take potshots at it.
Winter Blast can help you quickly dispatch a Big Daddy, as it stuns them and reduces the amount of damage needed to destroy them. However, their corpse will shatter, leaving no loot.
Security Bullseye can single-handedly take down a Big Daddy if you performs the following strategy:
First of all, hack a nearby machine and direct the flow towards an Alarm Tile.
Paint the target Big Daddy with Security Bullseye (Note: as this deals no direct damage, this won't cause the Big Daddy to attack you in any way).
By the end of the alarm, the Big Daddy will be either severely weakened or dead, without you risking themselves at any point. Note: This strategy is more effective on Bouncers as they cannot destroy Security Bots unless they stray too low.

Recommended Weapons and Ammunition

Electric weaponry such as Electric Gel and Electric Buck are the best form of ordnance against Big Daddies: not only do they deal much more damage against them than with any other ammo type, but they also temporarily shock Big Daddies, stunning them.
Armor-piercing ammo also deals increased damage against Big Daddies, although not as much as electric ammunition.
Exploding Buck deals very high amounts of damage and sets the target on fire, making it a very good choice in this type of fight. On Hard, no more than six shots are required to kill any Big Daddy on any level.
Frag Grenades and Heat-Seeking RPGs, because of their high damage output, are a useful tool against Big Daddies. Note: If tackling a Bouncer, it is better to have the upgrade that renders you immune to self damage, otherwise you may end up losing a lot of health.
Proximity Mines are incredibly versatile when it comes to Big Daddies. One of the most popular strategies involves attaching several Proxy Mines onto a physics object (preferably an explosive) and firing it at the target Big Daddy using Telekinesis. This is called an "Anti-Big Daddy Bomb", as it usually ends up killing or at least severely weakening the aforementioned victim.
Napalm, although not as effective as Electric Gel, is nevertheless capable of taking down a Big Daddy in a couple of seconds.
Liquid Nitrogen presents the same characteristics as Winter Blast, and both can be used interchangeably. Using a full tank of Liquid Nitrogen (or 50 units if upgraded in ammo efficiency) will keep it frozen long enough for you to shatter it. Although a safe and relatively fast way of killing the Big Daddy, it will not drop any loot, just like anything else that's shattered. (Big Daddies tend to drop rare U-invent items and around $70).
Although headshot bonuses do not apply to Big Daddies, Steel-Tip Bolts and Incendiary Bolts (especially the latter) are still capable of dealing high amounts of damage to Big Daddies.

Recommended Tonics

The Armored Shell line of Tonics will significantly reduce damage received by a Big Daddy's attacks, making this a very useful Tonic to have during combat.
EVE Saver will reduce the cost in EVE when casting Plasmids.
The Damage Research line of Tonics will significantly increase damage dealt against enemies researched using the Research Camera. The effectiveness of this Gene Tonic is entirely dependent on how much research you have done.
The Medical Expert line of Tonics will help you save up on First Aid Kits.
The Electric Flesh line of Tonics, in addition to makingyou resistant or even immune to electrical damage, will significantly increase the effectiveness of all electricity-based attacks.
The Human Inferno line of Tonics increases fire resistance in addition to damage from all fire-based attacks, in case you prefer incendiary ammo.

General
Bouncers are clad in a very distinct heavy diving suit, the entire torso of which is covered by a thick metal carapace. The head protrudes directly forward from the upper chest area, and is encased in a hemispherical helmet studded with eight lit portholes. A large, fully-functional conical drill is attached to the right arm just forward of the elbow, and is used for powerful melee attacks. The Bouncers get their name from their will to protect their bonded Little Sisters.

Elite Bouncer










In addition to normal Bouncers, you will encounter Elite Bouncers, which use a spinning harpoon instead of a drill, are decorated with red stripes, and are more difficult to deal with than the earlier Bouncer. The regular Bouncers are encountered in Welcome to Rapture and the Medical Pavilion. The Elite Bouncers are present in Fort Frolic, Hephaestus, and a single one in the Proving Grounds.

Attacks

When in combat, the Bouncer will produce three different kinds of attack:
Drill Slam: In this attack, the Bouncer slams the ground with its drill, causing a tremor in the surrounding area and disorienting anyone in the radius. Usually the Bouncer will follow this up with a Charge; the foe will be too sluggish to avoid it.
Drill Punch: This is the Bouncer's basic attack, it is accomplished when it drills into its foe. If against a Splicer, the victim is killed instantly. The attack deals a severe amount of damage to you, killing you instantly if you are low on health.
Charge: If the victim is far from the Bouncer, it will charge at them at high speed. This knocks the foe back, dealing them damage in the process.

Strategy against Bouncers

When starting a fight, always try to assault a Bouncer from a ledge, or at least ensure the Bouncer will take some time to get to you. In this fashion, you will be able to take free shots at the Big Daddy before he can get a chance to hit you. In close proximity (BD in melee mode), by jumping back and forth over an obstacle (ex- the counter in Medical Center on upper level with the cash register on it) you could throw off the Big Daddy to stop his physical attacks. While it is again moving to reach you, you fire at him long enough to kill him. Repeat if needed.
When charging, Bouncers cannot change their path, and will continue in a straight line no matter what. Not only can you use this to dodge their attack, but you can also exploit it to set traps into a Bouncer's path and provoke them into charging through them.
Bouncers always take the shortest route to you, making their movements very predictable. This can be used to your advantage in a variety of ways, such as when placing traps or when aiming at the Bouncer.
One of the main strategies the Bouncer relies on is disorientation. If you can keep a cool nerve and steady aim, you wield a significant advantage over this enemy type.

Recommended Plasmids

Cyclone Trap, although it has no effect on Big Daddies, prevents them from passing through the vortex. This can be used to prevent a Bouncer from getting to you, for example by setting up a wall or a protective ring around yourself (or the Bouncer).
Target Dummy can be used to lead a Bouncer to charge into a trap (for example, by setting a trap under or behind the dummy). This also temporarily distracts the Big Daddy.

Recommended Weapons and Ammunition

Trap Bolts and Proximity Mines are particularly effective against Bouncers, as they can be fired onto their movement path. You may also lay the traps and then proceed to coerce the Bouncer into charging through. In the case of Proximity Mines, placing several explosives near the mine will save ammunition.
Liquid Nitrogen allows you to stop a Bouncer's charge attack instantly, which is useful when you're is stunned and dodging it is difficult. This tactic uses only a few units of fuel, costing far less than Plasmids. With a full tank of fuel you will likely never need to reload during the fight, avoiding the delay of having to refill EVE after every few Plasmid uses.

Recommended Tonics

The Static Discharge line of Tonics will damage and stun any nearby enemy upon receiving a melee hit. Do not equip this if you wishe to use Hypnotize Big Daddy, as merely bumping into the Big Daddy will cause a discharge, and turn it against you.
The SportBoost line of Tonics will help you dodge the Bouncer's charge attack, as well as escape from it.

Stats
Health
Normal Bouncer - 2750 , Elite Bouncer - 4100
Damage
Bouncer's Drill - 100
Bouncer's Charge - 140
Elite Bouncer' Drill - 150
Elite Bouncer' Charge - 200

Research Rewards

1) + Damage Vulnerable to Armor-Piercing Rounds
2) Wrench Jockey 2- Increases damage dealt by the Wrench by 550%.
3) ++ Damage
4) Wrench does +50% damage to all enemies
5) +++ Damage

General

Rosies are clad in a basic heavy flexible fabric diving suit, the upper torso of which is covered by a high-gauge metal carapace. The head is guarded by a thick metal diving helmet welded to the torso carapace, and has three large lit portholes. They wield large Rivet Guns and Proximity Mines at long range, and use the Rivet Gun for powerful melee attacks as well. Rosies are also the supplementary mechanics and maintenance workers of Rapture. Their main weapon is a giant Rivet Gun. They are taller and slower moving than the Bouncer, making them less agile, but their long-range gun makes them just as dangerous.

Elite Rosie
Starting in Olympus Heights, you will begin to encounter Elite Rosies, which are significantly more powerful than their original counterparts, and with 50% more health. The Elite Rosie has a large, red collar.





Attacks

Shoot: The Rosie's basic form of attack, where it shoots the target repeatedly with its Rivet Gun.
Mine Throw: If an enemy approaches the Rosie, it will start throwing Proximity Mines at the target.
Push: If the Rosie's foe is at melee range, it will push them away with their Rivet Gun, dealing medium damage.

Strategy against them

Keep in mind that Rosies are the most heavily armored enemies in the games, more so even than Bouncers. As such, be ready for a prolonged fight, and try to completely isolate the Rosie from its surroundings before attacking.
Rosies are very accurate shooters, and are capable of dealing heavy damage if you aren't careful enough. Always try to attack a Rosie where there is plenty of cover to be found, and avoid open spaces.
When at mid-range, always stay on the move, as the Rosie will start throwing Proximity Mines at you.
Moving in a circle around a Rosie at close ranges will greatly decrease its chance of hitting you.
Although Rosies aren't as specialized in melee combat as their Bouncer counterparts, they are still capable of inflicting a severe amount of damage to you and will knock you back whenever possible. As such, use stunning Plasmids when attacking the Rosie at close range.

Recommended Plasmids

Telekinesis is more effective against Rosies than Bouncers, due to the increased number of possible strategies:
You can use it to create movable cover and a shield by picking up and holding a large, solid object.
By approaching a Rosie and firing its Proximity Mines back at it, you will be able to kill them without receiving any damage, and at a minimal cost in EVE.

Recommended Weapons and Ammunition
Electric weaponry such as Electric Gel and Electric Buck are the best form of ordnance against Big Daddies: not only do they deal much more damage against them than with any other ammo type, but they also temporarily shock Big Daddies, stunning them.
Armor-piercing ammo also deals increased damage against Big Daddies, although not as much as electric ammunition.
Exploding Buck deals very high amounts of damage and sets the target on fire, making it a very good choice in this type of fight. On Hard, no more than six shots are required to kill any Big Daddy on any level.
Frag Grenades and Heat-Seeking RPGs, because of their high damage output, are a useful tool against Big Daddies. Note: If tackling a Bouncer, it is better to have the upgrade that renders you immune to self damage, otherwise you may end up losing a lot of health.
Proximity Mines are incredibly versatile when it comes to Big Daddies. One of the most popular strategies involves attaching several Proxy Mines onto a physics object (preferably an explosive) and firing it at the target Big Daddy using Telekinesis. This is called an "Anti-Big Daddy Bomb", as it usually ends up killing or at least severely weakening the aforementioned victim.
Napalm, although not as effective as Electric Gel, is nevertheless capable of taking down a Big Daddy in a couple of seconds.
Liquid Nitrogen presents the same characteristics as Winter Blast, and both can be used interchangeably. Using a full tank of Liquid Nitrogen (or 50 units if upgraded in ammo efficiency) will keep it frozen long enough for you to shatter it. Although a safe and relatively fast way of killing the Big Daddy, it will not drop any loot, just like anything else that's shattered. (Big Daddies tend to drop rare U-invent items and around $70).
Although headshot bonuses do not apply to Big Daddies, Steel-Tip Bolts and Incendiary Bolts (especially the latter) are still capable of dealing high amounts of damage to Big Daddies.

Recommended Tonics

The Armored Shell line of Tonics will significantly reduce damage received by a Big Daddy's attacks, making this a very useful Tonic to have during combat.
EVE Saver will reduce the cost in EVE when casting Plasmids.
The Damage Research line of Tonics will significantly increase damage dealt against enemies researched using the Research Camera. The effectiveness of this Gene Tonic is entirely dependent on how much research you have done.
The Medical Expert line of Tonics will help you save up on First Aid Kits.
The Electric Flesh line of Tonics, in addition to makingyou resistant or even immune to electrical damage, will significantly increase the effectiveness of all electricity-based attacks.
The SportBoost line of Tonics will make it easier for you to run for cover as well as dodge the Rosie's attacks.
Static Discharge will help when struck by a Rosie as there is a good chance they will be shocked and give you a chance to get away.

Stats
Health
Normal Rosie - 3300 , Elite Rosie - 4900
Damage
Rosie's Gun - 70
Rosie's Melee and Proximity Mine - 120
Elite Rosie's Gun - 100
Elite Rosie's Melee and Proximity Mine - 180

Research Rewards

1) + Damage Vulnerable to Armor-Piercing Rounds
2) Photographer's Eye 2 - Increases all research photo scores by 15%
3) ++ Damage
4) Rosie loot almost always contains rare Invent parts
5) +++ Damage