Collectibles

At the end of each level, the game gives you a score based on how many stars, red coins and flowers you collected. Each star and red coin is worth 1 point and flowers are worth 10. In Any% speedruns, these collectibles are purposely skipped because they take extra time to be counted on the score screen and are simply not needed. In 100% however, it is required that you complete each level with 30 stars, 20 red coins and 5 flowers. Completing each level in a world with a score of 100 will unlock an extra level for that world and it is also required that... on each of these levels.

Each level has 20 red coins and 5 flowers hidden at fixed locations and serve no real function other than being mere collectibles. Stars however, act as Yoshi's health and increase the timer that counts down when you get 

Stars File:Star.png

Stars serve as health, increasing the timer that counts down when Yoshi is hit by 1 unit per star and is capped at 30. This prevents Baby Mario from being taken away from Yoshi as soon when hit. There are fixed locations in levels to get bundles of stars, such as winged clouds (3 or 5 stars depending on the cloud), crates/boxes (6 stars), tulips (8 stars) and middle-rings (10 stars). Having more than 20 stars when collecting a middle-ring will shorten the freeze that it causes by 8 frames per star. If a middle-ring is not able to be skipped, it's preferable to have as many stars as possible. 2 stars can also be spawned if Yoshi hits an enemy or other interactive sprite with a red egg. Stars are collected on contact and can also be tongued by Yoshi. There is theoretically no limit to the amount of stars available in a level as long as you can make red eggs and hit something with them. In 100% speedruns, you must finish every level with 30 stars, which would give you 30 of the 100 points needed. In Any% speedruns, stars are available as a "safety net", but are usually ignored. [1]

Red Coins File:Redcoin.gif

Red coins are disguised as normal, yellow ones. However, while they are disguised, they have a reddish tint. (Some normal coins have a red tint as well). They are also slightly larger than the yellow counterpart, allowing for easier collection. There are 20 red coins in each level and in 100% speedruns, you must finish the level with 20 but you can duplicate red coins to skip slower ones. This would give you 20 points towards the 100 total. In Any% speedruns, it's best to avoid these, as their listing on the score screen takes a few frames.
*3-E has 21 red coins. It's most likely the one hidden in a post underneath a Tap-Tap.[2]

Flowers

There are five flowers in each level. Some are out in the open, some are hidden in winged clouds and others can be earned through destroying all the enemies in specific rooms. They can be collected by touch or by contact with a thrown egg or a spit out enemy. In 100% speedruns, you must finish each level with 5. This gives you 50 points towards the 100 total, plus an extra life. In Any% speedruns, flowers are avoided because they can trigger bonus challenges as well as add extra time to the score screen.
*5-7 has six flowers. The sixth one is hidden off-screen but can still be collected with an egg. This is actually used in 100% speedruns to skip a much slower flower. [3]