What does Downwards Button look like on HTC?

On HTC it is the design shipped in Sense 8, shown above at full size. Older revisions are listed beneath it.

When did HTC add Downwards Button?

HTC first drew Downwards Button in Sense 7, released March 30, 2015.

HTC Corporation has shipped 2 versions of Downwards Button. Each is dated, so you can see when the design changed.

HTC

HTC Corporation has drawn Downwards Button 2 times. Every revision HTC has shipped is below, newest first.

What does Downwards Button look like on HTC?: On HTC it is the design shipped in Sense 8, shown above at full size. Older revisions are listed beneath it.
When did HTC add Downwards Button?: HTC first drew Downwards Button in Sense 7, released March 30, 2015.
How many times has HTC redrawn Downwards Button?: HTC Corporation has shipped 2 versions of Downwards Button. Each is dated, so you can see when the design changed.

HTC artwork for this emoji spans 2015 to 2016.