This hoverboard doesn't have any unlockable upgrades.
Splash is a limited hoverboard released with Subway Surfers World Tour: Buenos Aires. Like any other hoverboard, it protects you from crashing for 30 seconds. When crashed, the hoverboard will explode and need to recharge for a few seconds before using again. Like most of others limited hoverboards, it costs 50,000. It resembles a jet plane.