This meter displays the playable Yoshi's health. Each petal on the flower is one point of health for the Yoshi; there are eight flower petals displayed, so the Yoshi being played can only take damage up to eight times before all of the flower's petals can be plucked. If that happens, the flower's face will frown and the music will slow down greatly in both pitch and tempo; this also means that the current Yoshi will faint and be taken to Bowser's Castle via Toadies if it takes an additional hit while the flower's frown is on display. If the current Yoshi is squished or falls into an abyss/bottomless pit, the flower will lose all of its petals and the Yoshi in play will get escorted. If the player's last Yoshi gets taken to Bowser's Castle, the game is over.
As the Smile Meter depletes, it becomes a sadder flower. The smile on the flower becomes a discomforted frown as it nears its end, having no petals to protect the Yoshi. If a Heart Fruit is eaten, then the Smile Meter grows an ecstatic, happy smile for a limited amount of time.
Yoshis can primarily replenish the Smile Meter by way of eating fruits. Depending on the color of the Yoshi, different fruits will replenish more pedals for the Yoshi. Grabbing Special Hearts or Heart Fruits can also heal a Yoshi's Smile Meter.