Leech Hunter is an unlockable minigame in Resident Evil 0. To unlock it, simply complete the main game regardless of difficulty.
The minigame is accessed by selecting "Extra" or "Extra Game" on the Load Game menu.
On Gamecube and Wii versions of the game, players have the option to select Rebecca's and Billy's outfits with the "COSTUME CHANGE" option. Rebecca's outfits are "NORMAL", "LEATHER", and "COWGIRL". Billy's outfits are "NORMAL" and "JACKET". This option is omitted in the HD Remaster.
The "HOW TO PLAY" menu option brings up the following explanation of the game:
Find all the "Blue Leech Charms" and "Green Leech Charms" in the Umbrella Facility and exit via the Mansion's front door!
Leech Charms Features:
1. Colors and Characters
Billy and Rebecca can only carry a certain color of "Leech Charm".
"Blue Leech Charms" =Billy only "Green Leech Charms" =Rebecca only (Cannot be exchanged)
2. You Cannot Leave Items
Once the player acquires a "Leech Charm", it cannot be left.
3. Number Storable in One Block
Ten "Leech Charms" can be stocked in one item block.)
4. Number of "Leech Charms"
Blue Leech Charms --50 Green Leech Charms -- 50
"They're definitely there, somewhere!"
5. Game Over
If you exit through the Mansion's front door, or if Billy or Rebecca are killed, then the game is over.
A dead character's objects are not counted, so be sure to stay alive to the end.
We wish you the best of luck.
"You must survive in order to expose this nightmare..."
— Message displayed when game begins
The minigame takes place in the Umbrella Research Center and its basement. Billy and Rebecca will begin the game with their respective Handguns, 200 Handgun Ammo each, and a First-Aid Spray each. Other weapons and health items are scattered about the map. There are two different possible gameplay patterns. Each pattern is chosen at random and affects item, leech, and enemy placement. The main difference between the two is that either the Sub-Machinegun or the Magnum will be in the dungeon room with the eliminators. The two variants can be distinguished immediately upon starting the game by looking at the two herbs in the main hall. Blue and green is the magnum variant; green and green is the Sub-Machinegun variant.
The majority of rooms are unlocked; however, some rooms are inaccessible, one door is locked from the other side (the one leading to the outside balcony from the central conference room), and there are two doors that need to be unlocked using the Fire Key, which is found either in the basement waterfall room with the two plague crawlers or next to the trainwreck. The rooms unlocked by the Fire Key are the downstairs kitchen and the room with the moose head mounted on the wall and zombies on the ground off of one of the central hallways (off of the conference room).
The amount of health and behaviors of most of the enemies are adjusted for the game. Zombies have much more health taking up to ten handgun bullets to drop, and tougher enemies have slightly less health, usually dying from a single grenade launcher shot plus a single handgun bullet. When the player's total leech count reaches 90, a respawn wave is triggered, causing some rooms to become flooded with enemies, even rooms that have already been cleared out. The respawn wave includes 21 zombies and one plague crawler in both the sub-Machinegun and Magnum variants. The plague crawler will spawn in the waterfall room where the two plague crawlers were and where the Fire Key can be found. The 21 zombies will spawn in the animal puzzle room, the kitchen, the outside balcony, the two central hallways off of the conference room, and the dark monitor room off the black spider hallway leading to the dungeon.
After exiting the mansion or upon death, the game will end and the results screen will be displayed. The number of leeches each character collected, the combined total, and average time taken to pick up the leeches will be shown. Last, the player will receive a rank based on the number of leeches they found and prizes for the main game based on their rank.
"You got the A Rank item, Infinite Ammo.
Any weapon you received during the game will have unlimited ammo."