In the lead-up to the Wii U's launch it had been widely reported that it would not be possible to use the built-in microphone on the Wii U GamePad for in-game voice chat and that verbally active online gamers would have to resort to using a dedicated headset if they are inclined to have their voice heard by fellow players. This turned out not to be true since even launch games like Mass Effect 3: Special Edition let players use the built-in microphone for voice that during gameplay with a push-to-talk function while Ninja Gaiden 3: Razor's Edge and Assassin's Creed III have an always-on setting for the mic. Apparently, the feature is only available on a case-by-case basis (at the discretion of each game's respective developer) but it is possible and already widely used in most Wii U titles with online play. The option to use a proper headset obviously still exists.
Other releases that supported this feature post-launch include Trine 2: Director's Cut (added via free content update) and Monster Hunter 3 Ultimate (via Day-1 patch).
The first Wii U title to use the game for anything other than voice chat is Deus Ex: Human Revolution Director's Cut which lets players annotate the in-game map with voice messages that can also be shared online via Miiverse.
In Super Mario 3D World, players can blow into the microphone to remove puffy pink cloud blocks hiding secret passages. This technique has often been used in Nintendo DS games previously. It marks the first use of this concept in a Wii U title.