By throwing an item upwards into a block it is possible to duplicate the block.
Carrying Two Objects
If 2 objects are placed in the same location, Mario is able to pick up and carry both objects by running into them.
By defeating enemies and loading and placing objects in precise locations in Yoshi's Island 2, it is possible to warp directly to the game's ending sequence. This is caused by the placement of the objects, which writes data into the game's memory and can be exploited to cause the warp.
Collecting a power-up on the same frame the timer runs out will allow the player to continue controlling Mario after the timer hits 0.
Re-Useable P Switch
When a P Switch is pressed, swallowing it with Yoshi or grabbing it and taking it through a Warp Pipe will cause to the P Switch to return to normal and can once again be used.
Yoshi Double Eat
Berry / Power-up Freeze
Collecting a stored item on the same frame as eating a berry with Yoshi will cause the game to freeze. This will cause Mario to flash from red to green similar to if he touched a Super Star. It can also infinitely raise the player's coins, giving the player up to 99 lives in the process.
This glitch can only be deactivated by quitting the level, or resetting the game.