Baron mount

Baron Rivendare's mount used to arguably be the rarest drop in the game:

Just to get an idea of how rare this is.. (taken from the WoWhead comment)

As of 2/2/2008, Wowhead has only seen 1 drop out of 5290 kills...

(1/5290) * 100% = 0.019%

For one run of a given instance, the odds are higher that...

*
Ashes of Al'ar drops (90x more likely)
*
Swift Razzashi Raptor drops (63x more likely)
*
Swift Zulian Tiger drops (31x more likely)
*
Baron's Runeblade drops (9x more likely)
*
You are audited by the IRS
*
You die from slipping in a bathtub
*
You have a life


Personally I've been playing on and off since release and have only seen it twice across two servers. I've seen the black bug mount (the reward for a lengthy quest line involving 40 man raids at the time) more than that.

Well recently they changed it to be 1 out of 100 chances. Since then I know of 2 people that have gotten it to drop. Now people are farming it like they'd farm herbs. I've tried a few times, don't know if I have it in me to keep at it. I believe it's an achievement as well so that will make it more popular.

I can see now whatever they make an achievement they tend to want to make it more possible that people can nibble the carrot. If you keep it on a pole on a string too far away players just get angry.