Gerd's Lucky Charm is a 2" diameter ivory circle, with a simple leather cord running through a hole in the charm. It's magic effect only works when worn around the neck. On one side, the name Gerd is carved into the surface, on the opposite side, Lucky. It appears to be written in the character's main language. If the character can't read, then they know it's Gerd's Lucky Charm, but not how to activate the effect.
If the charm is touched, and the character says, "I need some luck.", or something similar, a modifier of 1 is applied to their next roll. If they need to roll higher than a target number, then it's added. If they need to roll lower than the target number, then it's subtracted. Any damage inflicted is increased by one. There is no limit to the number of times a day this ability can be used.
However, if the character doesn't use Gerd's Lucky Charm for an entire day, then the next day is a cursed one. For every roll the character has to make, a modifier of 2 is applied. If they need to roll higher than the target number, then it's subtracted. If they need to roll lower than the target number, then it's added. Any damage inflicted is reduced by 2. It doesn't matter if the player tries to activate it's normal luck bonus, the day will be an unlucky one.
If a character dies due to an unlucky roll, the charm will disappear. It has teleported to a random location.
The next day, after a cursed, unlucky day, the charm's effect returns to normal. If the luck isn't used that day, then the next unlucky day, the modifier is raised to 3. This will continue until the unlucky modifier reaches 6. If it isn't used the day after reaching the modifier of six, it teleports away. Gerd's Lucky Charm wants to be used for luck.
Only one Gerd's Lucky Charm exists.
NOTE: The modifiers can be changed to fit into whatever rule set you use.