As for the original question, refluff the riding horse.
(Also, the 4E version will not actually be called a mule, but rather a Donkeyhorse.)
I think Rel was in charge of the mule. And, well, he was . . . irresponsible. So therefore, no more mules.
Bullgrit
(Also, the 4E version will not actually be called a mule, but rather a Donkeyhorse.)

Surely you mean a Warbearing Donkeyhorse.
Surely you mean a Warbearing Donkeyhorse.
Now we've got it 4Eified!And they don't even include the price of whores!

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.