How do I upgrade my duck?
Solution 1:
The duck maintains it's own version of a kill streak (a duckstreak). Creating ducks, and picking up ducks gathers XP. If your XP reaches 5000, the duck will level up, and the XP will be reset to 0.
This works very similiar to strange weapons. When the duck levels up, it will get another title, just like a strange weapon does.
The Duck Tokens increase the amount of ducks dropped for each kill, objective, etc. This will allow you to level up your duck faster.
That's all there is to ducks. More can be found here: https://wiki.teamfortress.com/wiki/Duck_Journal