There is a way to get to the floating island at Bob-omb Battlefield with Yoshi. Follow these steps.

Step 1: Go to the cannon on the summit. It's by the wooden plank.
Step 2: Get in the cannon.
Step 3: Aim a bit over the tree, then shoot yourself.
Step 4: Hope you land safely!!

You will most likely land on the platform. If you don't, try again. It'll work sometime!