When you fight the Leech Zombie, its legs will swell up at the end and explode, hurting and often killing you or your partner. There are three ways to avoid this. First, just run through a door as his legs are swelling but before he explodes. Make sure that nothing is attacking you or your partner when doing this. Return to the room and there will be no extra leeches. The second is to use a Molotov cocktail on him, which will light him on fire and melt into a puddle of slime and leeches. The third is to kill him while he is still in "human" form, which is best done with the magnum and has the end effect as the Molotov cocktail.
Better hunting gun use
If you have the hunting gun with unlimited ammunition from Leech Hunter mode, equip Rebecca with it. She shoots faster than Billy. Billy shoots once per second, while Rebecca can shoot about two or three times per second.
Better shotgun use
Once you get the shotgun, do not use it. Instead, leave it in the room with the scale you put the two figures on. Find, but do not pick up, lots of shotgun ammunition. After you save her from the pit, give all the hand gun ammunition to Billy and collect the shotgun ammunition. If you get it all, she will have about 60 rounds, which is much better than using two hand guns.
Chess puzzle solution
Look at the smaller chess board on the desk in front of the big one. Arrange the big pieces the same way. The difference is the only white piece by itself. Use Billy to push it down, to the right, and finally right in front of the black piece. The desk will now open.
Custom handgun
When you are in the draining room in the facility basement, you will find the Duralumin case. You have to enter a code, which is "385". The case will open and you will find handgun parts. Combine these with Billy's handgun for a more efficient handgun.
Dial door number puzzle
Enter "4863", where the cable car is located.
Easier game
When you start the game as Rebecca, get to the point where you meet Billy. He will say that they need to cooperate. When Billy joins you on your mission, it is best if you have him in control at all times since he has stronger defense and will not get damaged as quickly as Rebecca. Note: This is the same in all modes.
Easy Leech Zombies kills in Hard mode
Throughout the game, you will find a lot of empty bottles. Do not ignore them. Pick them up and combine them with the gas can for the Molotov cocktails. Two of these will take out a Leech Zombie. Also, it will not explode as usual; you no longer need to run away. It will also kill a zombie with one hit or two zombies at once if you hit directly between both of them. Note: This weapon can harm you or your partner if thrown too closely.
Extra inventory slot
While playing as Billy with Rebecca as the alternate character, have Billy hold all the pistol ammunition for both characters and keep her gun fully loaded. This gives you one free inventory slot.
Killing zombies
While using the shotgun, aim down at the zombie's legs and shoot it. He will fall. Then, take out the handgun and shoot him one more time.
One-hit kills
While playing as Rebecca or Billy and you get bit by a zombie, move the character opposite of your main character directly behind the one you are controlling to have him or her shoot the zombie in the head and kill it in one hit, while the zombie deals you no damage. Note: You must have pistol equipped to save ammunition for a one bullet kill.
Pause timed puzzles
Try to change to your partner during a timed puzzle. Remain idle at the error message to give yourself more time to study the puzzle.
Safer and faster shotgun reload
To reload the shotgun quicker, go to the item screen. Combine the shotgun ammunition with the shotgun. You will be able to attack again without having Billy or Rebecca reload and waste precious time.
Save ammunition on first Leech zombie on the train
After the sequence with the first Leech zombie, just go back downstairs and the intermission sequence will take place again.
Saving ammunition
Equip the handguns to both Rebecca and Billy. Control Billy. When you see a zombie, shoot him until he falls, but do not kill him. Then, equip the pocket knife and kill the zombie with it. This will save about two to five bullets each time.
There are two knife methods you can use to save ammunition for the Bosses. The first method is used fighting solo without the help of Billy or Rebecca; depending on whom you use. Make sure you keep about two steps away from the zombie and aim downward with your knife. Slice him once and he will make a failed attempt to lunge at you. Then, slice his feet again and he will fall down. Once down, do not knife him anymore. Instead, take about a step backward and wait for him to get up and repeat this process again. This method works if there are multiple zombies. Alternately, if there is only one zombie you move to behind the zombie's head when he is laying down. Then, knife his head and keep knifing him as he gets up. When done properly you will knife his feet twice and he will fall down again. This will allow a few extra shots in as you knife his head while he gets up. The second knife method is used fighting with a team. The person you control should be using a knife, and either Billy or Rebecca should be using a gun (and set on attack mode). Get in front of the one with the gun and knife the zombie's feet. As you knife the feet, your partner will shoot the head and the zombie will fall down. Then, go over and knife the zombie while he is on the ground. As he gets up, keep knifing him and your partner's help will assist you in finishing him off properly.
Train items
There are items in the train. If you do not need them, select them but do not take them. When the train crashes, items will be scattered around the wreck. Those are the items that you selected. The items not selected will disappear. This is very important if playing on the Hard difficulty.