Yoshi's main weapon is his improperly large tongue. With it, he can eat practically any enemy on the screen and turn it into an egg that follows behind in a pied-piper fashion. Tapping the attack button brings up a targeting reticule - line up enemies, floating items or other targets to strike them. There are tons of well-hidden paths to find by ricocheting eggs around the levels and tagging suspicious-looking objects. Opening up each level is part of the series' enduring, if a little kiddy, charm.
And, of course, at the end of each multi-leveled world is a boss. In the E3 demo we played, it was some kind of bouncy bulb thing with balloons all over it. Bursting the balloons, for whatever reason, caused the thing great physical pain. So we thrashed them all and it promptly died.
Yoshi's Island 2 is not going to change the world. It should, however, offer up the same level of spot-on control and crayon-quirky graphics that its predecessor did so many years ago.