Message Block

Hint Blocks, also called Message Blocks, Chatter Boxes, Tip Blocks, and Face Blocks, are blocks with faces that appear in various platformers. They are most prevalent in the Yoshi series. They are usually white, smiling blocks that give provide tips and hints to the player when hit.

Super Mario World
Hint Blocks first appeared in Super Mario World, where they usually described a new level in the beginning stages of the game or explained a new game mechanic. Unlike later appearances, Hint Blocks had no face in Super Mario World but instead they looked like speakers.

Super Mario Bros. Deluxe
Despite not appearing in Super Mario Bros. they did appear in its Game Boy Color remake, in the versus mode, two versions of Hint Blocks appear. The white, smiling ones are good, while the red ones, which stick their tongues out, make the level harder. In this game Hint Blocks are very different in that they don't actually give hints and are just obstacles rather than anything.

Super Mario World 2: Yoshi's Island
Hint Blocks became more common in the Yoshi series starting with Super Mario World 2: Yoshi's Island, where they taught the player controls and gave tips rather than saying things outright. Super Mario World 2: Yoshi's Island gave Hint Blocks their now-common look of smiling white faces.

Yoshi's Story
The Hint Blocks returned once more in Yoshi's Story here they filled the exact same role as they did in Super Mario World 2: Yoshi's Island. There appearance has changed since then though and they are now much bigger and the mouths are countinually moving.

Yoshi's Island DS
They returned in Yoshi's Island DS and were much the same as before but return to their Super Mario World 2: Yoshi's Island form.

Super Smash Bros.
Hint Blocks have a cameo in Super Smash Bros. this is in Yoshi's Island where one can be seen along with the Super Happy Tree.

Super Princess Peach
In Super Princess Peach Hint Blocks return to just giving hints when hit, though here they were yellow and were called Perry Blocks, in reference to the umbrella of the same name.

Trivia

 * In the Brazilian instruction manual for Super Mario World, the Hint Block is erroneously translated as 'massage block'.