From the announcement:
In Yoshi's Island Zone, Sonic must race across Yoshi's world in a brand new action-packed level. As you speed through this level, both Yoshi and Sonic players will notice some familiar items including pipes, coins, piranha plants and even Sonic's iconic loop de loops, all in the unique graphic style of Yoshi's world. Can Sonic find all the Yoshi's eggs to save all of the Yoshis? Well you'll need to explore the whole level to discover hidden areas to uncover these.