Blue Gem

The Blue Gem is is an optional upgrade for Sonic the Hedgehog in Sonic the Hedgehog (2006) and is one of the seven customized Gems that can be obtained in the game. It allows Sonic to use Mach Speed and dash forward. When in use, the Blue Gem changes the appearance and colors of Sonic's Power Sneakers into a blue pair of new shoes.

Location
In Sonic the Hedgehog (2006) the Blue Gem becomes available at the local shop, once the player clears Tails' version of the Wave Ocean in the main story. It can then be bought for 7000 Rings.