Go to the Lost Fleet in Wetlands and get the debuff from mobs while you are formed into boomkin / any other.
If you can use items (like pots) in your desired form, it means you can mount in it. While you are undead, and for example a boomkin, you can mount up and wait for the debuff to go away. You will then be a boomkin on mount, perhaps a flying one if you want.
As for Ghost Wolfs, you can not use items and therefor not mount. But while you are in the Undead form as a Wolf, you can wield your weapons. While you can not cast your spells or totems, you will be able to run in constant 40% and proc windfury.
Debuffs will stay when you enter an arena. Perhaps the negative stats of the debuff might not make it worth it, but maybe you can find a profittable exploit from it.
If you are in bear form, you can run around like a UD, wielding wep, and still use your charge/whatever bear attacks.
This is old, yes. But if you know this, don't assume everyone does. I found a couple of other threads, but they either used outdated ways or angled in a different direction