Every so often a tradition survives not because anyone celebrates it but because everyone remembers it. Mischief Night is the northern English institution of one evening's licensed misbehaviour, and it has more names than almost any custom in the country.
The names
In Yorkshire alone it has been recorded as Mischievous Night, Miggy Night, Tick-Tack Night, Corn Night, Trick Night and Micky Night. Around Liverpool it is Mizzy Night, familiar enough to Merseyside Police that they have patrolled for it.
The variety tells you how local and how oral this is. Nobody organised Mischief Night. It passed between children, and the name changed every few valleys.
The date is not what you think
Here is the detail almost every article gets wrong. Mischief Night is traditionally 4 November — the night before Bonfire Night, not the night before Halloween.
It has shifted. 30 October is now more common, pulled across by the gravity of Halloween, but the older northern English date sat squarely in the Guy Fawkes season. One historian's account has children looking to the opposite end of the year from the earlier May-time custom and settling on the eve of the Gunpowder Plot; the earliest reference is from Oxford in 1790, when it fell before May Day. The move to November happened only in the late nineteenth century, and is frankly described as one of the mysteries of the folklore calendar.
So if your grandfather insists Mischief Night was "the night before Bonfire Night", he is not misremembering. He is more correct than the internet.
What it involved
Pranks, of the labour-intensive rural sort. Tick-tack — the name behind Tick-Tack Night — involved a pin, thread and a button rigged to tap repeatedly at a window while you hid out of sight.
Gates came off their hinges in quantity. After a busy Mischief Night in 1930, the Yorkshire Post reported dozens of farm gates lifted off and hidden about the fields. Doorknobs were tied together, chimneys blocked, and signs swapped between shops.
The modern version, where it survives, is flour and eggs, and is considerably less charming. There is a real distinction between a village prank that takes ingenuity and an egg thrown at an elderly neighbour's window, and it is the reason the tradition has largely been suppressed rather than celebrated.
Why it existed
Mischief Night belongs to a broad European pattern of licensed misrule: an appointed window in which the usual hierarchy is inverted and the young are permitted to be a nuisance without lasting consequence. The pressure valve, in other words. It is close kin to the threat half of trick-or-treat — and the American formula almost certainly borrowed from it, fusing English mischief with the English and Irish tradition of souling at the door.
If you would rather your children were frightened than fined, we can suggest somewhere to take them.