This hoverboard doesn't have any unlockable upgrades.
Casket is a limited hoverboard, released with Subway Surfers World Tour: Mexico. Like any other hoverboard, it will protect you from crashing for 30 seconds. When crashed, the board will explode and recharge for a few seconds before it can be used again. It is a little coffin with a skull and a lock on it. Like most of others limited hoverboards, it costs 50,000.