If you mix: GREEN HERB + RED HERB + YELLOW HERB. It restores your health completely and raises your max health.

Each weapon has a special "exclusive power" when all of its stats are custom tuned to the maximum:

Handgun - Increases the chance of a headshot being fatal by a factor of five.
Punisher - Each bullet can penetrate up to five bodies.
Red 9 - Increases firepower to 5.0
Blacktail - Increases firepower to 3.4
Matilda - Increases magazine capacity to 100.
Shotgun - Increases the effective damage range of the gun.
Riotgun - Increases firepower to 10.0
Striker - Increases magazine capacity to 100.
Rifle - Increases firepower to 18.0
Semiauto Rifle - Decreases firing speed to 0.40 seconds.
Broken Butterfly - Increases damage to 50.0
Killer7 - No exclusive power!
TMP - Increases firepower to 1.8
Minethrower - Adds homing ability to mines and increases their blast radii.

Beat the game to unlock the mercenaries mini game.

Ada Wong: Get a 4 star rating on the Pueblo map of the game.
Albert Wesker: Get a 4 star rating on the Waterworld map of the game.
Hunk: Get a 4 star rating on the Island Commando map of the game.
Jack Krauser: Get a 4 star rating on the Castle map of the game.

Beat the game to unlock the mini game: Assignment Ada.