Unit fillers are mini-dioramas or other unusual things that people put into their regiments. Sometimes it's done to bulk out the regiment up to a certain amount of figures. Other times it's done entirely for looks.

They don't modify the rules for the regiment at all, they simply take the place of a certain number of troops. It's almost always done in the center of a regiment and done so that it can easily be pulled with other casaulties as needed.

Some examples:

A herd stone in a regiment of Bestigors.

Dwarf rune pillars each taking up one base on the four corners of a special dwarf unit.

A mounted preacher in the middle of a Empire unit extolling the blessings of Sigmar.

A pony and ore cart in a unit of Dwarf Miners.

A big squig in a goblin unit.

So what are your thoughts?