There are dozens of items in this game. Lets have a look.
Egg: You collect these throughout the game. You can collect them or eat enemies to get them. If you press the A button then Yoshi will start aiming the egg and, depending what mode you have it on, press A again or release A to throw it. Hold the L or R buttons to stop the egg aiming cursor from moving.
? Cloud: These appear around the game (and some don't until hit by something or Yoshi). Hitting them with an object... usually an egg... will set off an event or release items for you to collect. They create much needed platform as well.
Yellow Coin: These coins add 1 to your coin tally. 100 gives you an extra life.
Red Coin: Aside from acting like coins like above, there are 20 of these in each level that each add an extra point to your total points tally. Some are hidden among Yellow Coins, some are in hard to reach places, some are being carried by Flyguys. They are very hard to find.
Flower: These giant flowers are usually in hard to reach places. They can be collected by eggs but it is often better to find them yourself. There are 5 in each level and they each add 10 points to your total points tally. They also increase your chances of getting a bonus level at the end of each world.
POW Block: This is very rare. If you hit it then everything around you will turn into stars. It first appeared in Mario Bros. for the arcade.
POW Icon: You collect these from the bonus games. Using them will turn all enemies around you into stars. You can only use them once.
? Cloud Icon: You collect these from the bonus games. Using them will turn all enemies into clouds with coins, stars or nothing in. If you are lucky you might find something better.
10 star icon: You collect these from the bonus games. Using them immediately gives you ten stars. If you are trying to get 100 points then try using these at the end of the level to fill up your star tally.
20 star icon: You collect these from the bonus games. They are much more handy than the 10 star icon if you are very low on life at the end of the level while you are trying to get 100 points.
stars: These are often littered around the level in ? clouds, Giant Flower Heads and middle rings. It is also possible to turn enemies into them by various means.
6 egg Icon: You collect these from the bonus games. You can use these during the levels to fill up your egg supply.
Magnifying Glass Icon: You collect these from the bonus games. They are very handy if you are trying to find 100 points because they show where all the red coins are hidden and all of the invisible ? clouds.
Arrow Clouds: If you shoot an egg at these then it will fire off in the direction the arrow is pointing.
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