The way game development works is that you often create assets during early development that eventually get replaced.
For example, you need a movement animation in the game as a prerequisite for pretty much anything else involving a character.
Usually, all those early assets will get replaced with their final versions later in development – at a time when all the details have been worked out (e.g. the character speeds have been fixed, their special attacks are known, etc.).
This is true for all kinds of assets. Animations. Sounds. Weapons, etc. We’ve mentioned that almost nothing about the UI is final – again, it’s much more important to get a functional and somewhat presentable prototype UI in place to allow development and testing of dependent features than it is to get everything beautiful, right and polished the first time.
There’ll be still quite a few of those kind of functional placeholders (such as the UI) in the game around PAX, but you’ll also see a lot of things that used to be placeholder in their final versions.