Marley was dead: to begin with.  There is no doubt whatever about that.  The register of his burial was signed by the clergyman, the clerk, the undertaker, and the chief mourner.  Scrooge signed it: and Scrooge's name was good upon 'Change, for anything he chose to put his hand to.  Old Marley was as dead as a door-nail.

Mind!  I don't mean to say that I know, of my own knowledge, what there is particularly dead about a door-nail.  I might have been inclined, myself, to regard a coffin-nail as the deadest piece of ironmongery in the trade.  But the wisdom of our ancestors is in the simile; and my unhallowed hands shall not disturb it, or the Country's done for.  You will therefore permit me to repeat, emphatically, that Marley was as dead as a door-nail.

For the rest of us.

Like most holidays Festivus is a totally artificial construction around a false narrative.

I think I'll spare you the feats of strength.

Boxing Day.

On the day after Christmas...

• In feudal times the lord of the manor would give boxes of practical goods such as cloth, grains, and tools to the serfs who lived on his land.
• Many years ago on the day after Christmas servants would carry boxes to their employers when they arrived for their day's work. Their employers would then put coins in the boxes as special end-of-year gifts.
• In churches, it was traditional to open the church's donation box on Christmas Day and distribute it to the poorer or lower class citizens on the next day.

Take your pick.