Colonel Reb: definitely outdated, possibly a little offensive. So he's gone. Introducing the new mascot for Ole Miss: a generic bear in a sun hat, associated with another state entirely.
Rebel Black Bear beat out two other pretenders in student voting: the Rebel Land Shark, personified as a man dressed up as Jimmy Buffett's beer, and the Hotty Toddy, personified as my uncle after a few too many drinks on Christmas afternoon.
The American Black Bear has a link to Mississippi's folklore. Teddy Roosevelt's refusal to shoot a captive bear (he had someone else do it) led to the invention of the Teddy Bear. Old Ben was a land-based, furry Moby Dick that terrorized the forest in Faulkner's short story "The Bear."
But do a little research, and there's only one subspecies that actually lives in Mississippi: Ursus americanus luteolus, the Louisiana black bear.
Sure, it's native to Mississippi, but it's still named for their Magnolia Bowl rivals. There are plenty of perfectly good official Mississippi state animals (Ole Miss Bottlenose Dolphins, anyone?).
Of course, you won't ever hear Ole Miss refer to him as a Louisiana black bear. He's Rebel Black Bear, which I suppose means the bear fought for slavery and states' rights. Maybe they should drop the "Rebel" moniker altogether? It's somewhat uninspiring to take your inspiration from the losing side in a war. That'd be like if Army's sports teams were "The Vietnam Vets."