Do mounted wargs charge the same way as regular cavlery ? Are there any special rules associated with them?

I believe the ways in which regular wargs differ from horses are:

Different profiles (wargs have higher strength)
They can stay on the table if their rider is slain and they pass a courage test

Otherwise they function as normal cavalry.

Fell wargs also have a few special rules which I'm not sure of

wargs can attack.

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In a hole in the ground, there lived a hobbit.

They follow the normal rules for cavalry, except for the rules Nic0 mentioned. In addition, riders take the better of their mount's stats when determining fight, movement, etc. This is a great boon for the original war riders, as it means their orc riders get a +1 to fight value--a considerable improvement!

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"Diplomacy is the art of saying 'nice doggie' until you can find a rock." -Will Rogers