A nuclear control rod.
This item may be used as a bonus action. For the next 5 minutes, the user deals and recieves double damage from all sources.
If used multiple times, this only adds the base damage to the amount dealt and recieved an additional time. For example, if an attack would deal 5 damage, one use would double that to 10, a second use would add another 5 to make it 15, and a third use would add another 5 to make it 20.
All levels of this item's effects end at the same time, 5 minutes after the earliest use.