The original Nike Mag from 1989, the one that was made for Michael J. Fox's character Marty McFly in Back To The Future II, is up for grabs on eBay via Shoezeum. Well, sort of. Shoezeum is selling only the left shoe, which measure a size 10 from heel to toe. 

The sneaker is badly deteriorated and extremely fragile, but that hasn't stopped the bids from skyrocketing over $18,000 with more than six days left on the auction block. As shown in the photographs, the plastic outsole separates from the shoe if you pick it up and the midsole is cracking and crumbling. According to the listing, some of the crumbles have been preserved in two small plastic containers.

Only a few pairs of the original Nike Mag were created, and this particular pair is reportedly from the collection of a longtime Nike employee. Nike sold 1510 Mags via auction in 2011, and released an additional 89 pairs (with power laces) via raffle in 2016. 

You can check out the full listing for the OG Air Mag right here.