Resident Evil 0

Alternate costumes:
Successfully complete the game with any rank under the normal or hard difficulty settings. Start a new game. A Closet Key will appear in your inventory. Use it to unlock the closet in the room where the Hunting Gun was first found to access new costumes for Rebecca and Billy.

Completion bonuses:
Successfully complete the game with a "B", "C", or "D" rank to unlock the Leech Hunter mini-game.

Successfully complete the game with a time between 3:31 and 5:00 for an "A" rank to unlock the Submachine Gun and Leech Hunter mini-game.

Successfully complete the game with a time of 3:30 or faster for an "S" rank to unlock the Rocket Launcher, Submachine gun, and Leech Hunter mini-game.

Note: To a rank after completing the game it must be played under the normal difficulty setting. You will not get ranked under the easy difficulty setting, but can still unlock the Leech Hunter mini-game.
Michael Lane.

Hint: One hit kills:
When playing as either 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.
Michael Lane.

Hint Killing zombies:
With the shotgun, aim down to the zombie's leg and blow it away. He will fall. Then, take out the handgun and shoot him one more time.
Frank Drebin.

Hint: Extra inventory slot:
When 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.
Michael Lane.

Hint: Dail door number puzzle:
Enter "4863" on Disc 2, where the cable car is located.
kevin kelley.

Hint: Chess puzzle:
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.
Chico and Bella.

Hint: Brake system puzzle:
In order to start the train brakes, you must find the Magnetic Keycard (lying on the train control panel in the front car) and you must choose a character to go through the train. Do not choose Rebecca to go through the train. There are too many zombies for her to handle, and she will die. It does not matter if you killed all the zombies in the train, as more will appear. Once you have reached the caboose, use a healing item if necessary. Activate the control panel by using the Magnetic Keycard on the panel. The game will randomly choose one of three numbers to display, and you must figure out what ten numbers add up to the displayed number. The three random numbers and their solutions are as follows:

36: 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 9
67: 9 + 9 + 9 + 9 + 9 + 9 + 9 + 9 + 9 + 4
81: 8 + 8 + 8 + 8 + 8 + 8 + 8 + 8 + 8 + 9

After doing this, take control of Rebecca and she will do the same thing (but you do not need the keycard). She also has a set of three random numbers to solve. However, unlike Billy, they will not display your current total. The second control panel's three random numbers and their solutions are as follows:

42: 4 + 4 + 4 + 4 + 4 + 4 + 4 + 4 + 4 + 6
53: 5 + 5 + 5 + 5 + 5 + 5 + 5 + 5 + 5 + 8
67: 7 + 7 + 7 + 7 + 7 + 7 + 7 + 7 + 7 + 4

You have now completed the puzzle.
Humancomputer42.

Hint: Fountain circle puzzle:
When you get to the fountain circle with the six animal statues on Disc 1, use Billy to light the statues in the following order: Deer, Wolf, Horse, Lion, Snake, Eagle.
Jesse Rosa.

Hint: Animal puzzle:
The solution for the animal puzzle is Deer, Wolf, Horse, Lion, Snake, Eagle.
Barrelracer6596.

Hint: 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.

Hint: Piano room:
When you get to the piano room, make sure you have both characters with you. Have Billy play piano. A door will open by the bar. Have Rebecca go in and take the battery. The door will close. Have Billy play piano again and the door will open.
Seifer6426.

Hint: Longer life:
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. Because he has stronger defense and will not get damaged as fast as Rebecca. Note: This works in all modes.
Justin Chitwood.

Hint: 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.
n caputo.

Hint: 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.
Seifer6426.

Hint: Better hunting gun use:
If you have the hunting gun with unlimited ammunition from the Leech Hunter mini-game, 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.
kyle hefferon.

Hint: Safer and faster shotgun reload:
To reload the shot gun faster, press Y to 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.
DaHeroofTime.

Hint: 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.
radical_sk8boarder82.

There are two knife tactics you can use to safe ammunition for the Bosses. The first tactic 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 then 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 any more. Instead take about a step backward and wait for him to get up and repeat this process again. This tactic 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 tactic 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.
Joseph Danielson.

Hint: 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.
Roxanne Jaso.

Hint: Items:
In the train there are items. 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 under the hard difficulty setting.
JOE ALVARADO.

Hint: Avoid Leech Zombie explosion:
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 leave as his legs are swelling but before he explodes. 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 way 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.
PureMarioExtract.

Run through a door when it is swelling. Make sure that nothing is attacking you or your partner when doing this, Return to the room and there will be no extra leeches will no one hurt.
Cyberlumbee.

Hint: Easy Leech Zombies kills in hard mode:
From the beginning of the game onward, 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.
Henry Diez.

Hint: Resident Evil 2 areas:
When you eventually get onto the moving cable car, after Billy is taken over the railing by an ape, go across the ravine and head up the pair of steps. You will enter a big room with a metal floor. This is the same area in Resident Evil 2, where you call up the platform train to head down into the main factory (and where you fight a stronger version of the William Birkin mutations). If you go towards the bottom of the screen and go down the lift and into the back room, you will find a television screen with a picture of a Tyrant. This is the same room where you see Mr. X walking towards the camera before smashing it. If you call up the platform and take it down, you will enter the factory sub-levels and walk into the room where Leon/Claire had to carry Ada/Shelly to the security room.
Jamie Weir.

Hint: Hard mode:
Use the following tips to complete the game in hard mode.
Ian Smith.

Use Billy all the time. He can take much more damage than Rebecca.

Leave Rebecca in the main hall. She just uses up ammunition and first aids. However, bring her the plants to mix for you.

Use a custom handgun, or if you dare, a knife to kill the tyrant. It is easy to run circles around him and shoot him in the head, or use the knife. It may require about 30 shots with the custom handgun to kill one.

Use the Magnum ammunition for the last Boss only.

Do not use the Pump Action Shotgun. It is weak. The Hunting Gun does more damage. Get it on the train and keep it.

Use Herbs only if you are really hurt bad.

Use Fire Grenades on the Leech People.

Use your Molotov Cocktails on the final Boss' third form, Tyrant, or Leech People.

Sometimes you can run pass the hunters and out the room without wasting ammunition, such as when you get the up key. The same goes for the Leech People. They are too slow if you use one person to run past them.

Hint: Leech Hunter mini-game bonuses:
Successfully complete the Leech Hunter mini-game with one of the following ranks to unlock the corresponding bonus.
Michael Lane.

"A" rank: Unlimited ammunition for any weapon
"B" rank: Magnum
"C" rank: Hunting Gun
"D" rank: Handgun
"E" rank: Submachine Gun

Hint: Leech Hunter: Collecting Leeches:
While playing the Leech Hunter mini-game, kill everything in the Mansion, Train Tunnel, and Basement before picking up any of the leeches. Once you pick one up, you cannot put it down. Each player can find a maximum number of 50 leeches (100 total leaches in the game). One item slot can only hold 10 leeches only -- be careful.
Michael Lane.

Once you get 95 leeches, zombies will start to come back to life. Collect the leeches in the mail hall, dining room, and the second floor room where you use the MO disc last so you do not get killed.
Ian Smith.

An easy way to complete Leech Hunter mode is to go through and kill all the enemies first, then return and collect the leeches. Note: Collect the leeches in the Basement area first to avoid the risk of revived Zombies.
Jacob Ryder.

In the far back of the kitchen are two leeches (a blue and green one). They are difficult to see at first.
Joe Alvarado.

Hint: Leech Hunter: Extra Submachine gun ammunition:
As soon as Leech Hunter starts, grab the first leech you see and run out. This will give you a clip to the machine gun.
Seifer6426.

Hint: Leech Hunter: Finding the shotgun:
When you are in the sewers, pick up the shotgun ammunition. Then, keep trying to pick up something and you will eventually find a shotgun.
Ryan Murray.

Hint: Leech Hunter: Determining weapon:
There is a way to determine if you will get the submachine gun or the magnum. Look at the two herbs in front of the stairs in front of you at the start of the mini-game. If the colors are blue and green, you will get the magnum. If the colors are green and green, you will get the submachine gun. The submachine gun can do what the magnum can and requires a lot less ammunition. Green and green is highly recommended.
ZuulRules22.

If you want the magnum on the Leech Hunter mini-game, load your game on Disc 1 (only if you have passed the game once and have unlocked the Leech Hunter mini-game), then play the mini-game. You will see a Green Herb and a Blue Herb, indicating that the Magnum is there. If you want the Submachine gun, load your saved file with mini-game on Disc 2 and play the mini-game. You will see two Green Herbs, indicating that the Submachine gun is in the game.
Luigi666.

Hint: Resident Evil Outbreak reference:
The area where the turntable is located is from Resident Evil Outbreak. The turntable, elevator, the door that has main shaft on the wall, and the Security Room are on Resident Evil 0. These items are on the Below Freezing Point level in Resident Evil Outbreak. Also, the giant hanger where you defeat the G-Monster on Resident Evil Outbreak is also located in Resident Evil 0.
Logan Livengood.

Glitch: Kill bat without bullets:
At the church run, past the bat then enter the save room. When you exit back out, you will find the bat dead.
travisemmons.

Glitch: Skip first Leech Zombie encounter:
When you find the first Leech Zombie, try to walk back down the staircase. You will advance to the cinematic that normally plays if you chose to fight it.