Through most of the game, you’ll be escorting the mysterious Elizabeth around the perils of Columbia, as you attempt to escape the city in the sky.
While you are her escort, you never need to worry about Elizabeth in combat. She knows how to stay out of trouble, so you can fight your enemies without stressing about her safety.
Throughout the game, Elizabeth can assist you in a number of ways and allow you to reach areas that Booker wouldn’t normally be able to traverse.
Assists
When you’re in trouble and running out of health, Salts, or ammo—or perhaps you even need some extra cash—Elizabeth will help you out by giving you items.
When you see a prompt, press 
/
, and she’ll throw the item in question to you. After Elizabeth throws you an item, she won’t be able to help you out for a while, so you should try to make her gift count.
Also, whenever you find a lot of money lying around or visit a vending machine, keep an eye on Elizabeth—she tends to throw some additional cash your way! Visit every vending machine you see, if only to have Elizabeth offer extra cash for your cause!
Lockpicking
There are many doors in the world that only Elizabeth, the master of unlocking, can open. Look for doors with a large lock over them—Elizabeth can open these, granting you access to the rare items located behind them! However, Elizabeth will not pick open any locks while you are in combat.
To open many doors, you’ll need to use consumable lockpicks, which are fairly scarce. Keep an eye out for them so you can get behind every locked door and collect every Infusion, Voxophone, and piece of Gear!
Pieces of another World
During your journey, Elizabeth shows you her ability to peer into other worlds using her gift to “Tear” into them. This ability can be a very helpful asset, giving you access to new powerful tactics and weaponry!
Tear types include:
Allies: Elizabeth can summon mechanized allies, including Machine Gun and Rocket Automatons, Mosquitos, and even Motorized Patriots!
Recovery: You see glimpses of boxes full of Medical Kits and Salts to fill your Health and Salts Meters!
Navigation: Elizabeth can create freight hooks out of nowhere, giving you the ability to maneuver around combat areas.
Weapons: Elizabeth can summon stacks of powerful weapons like RPGs, along with plenty of ammo.
Traps: Elizabeth can summon pools of oil and water from other worlds, which you can use to create deadly flaming oil slicks using Devil’s Kiss or electrocuted puddles using Shock Jockey!
Decoy: Create a decoy to divert enemy attention while you take them out.
Cover: Create cover from nothing to put something between Booker and his enemies and take a breather during combat.
Stores: In two places you’ll find two Tears that give access to discounted Stores, one of which has discounted weapon upgrades!
There are other types of Tears, each of which compounds Elizabeth’s secret past.