Yes Aeonaxx ,the Very rare Spawn in Deepholm.
And lucky me ,here is the story of what happened :

On my main i went to Deepholm for the Elders Ach & bam Aeonaxx pops up on my NPC Scan addon. After a Year ,this was 1st tme i saw it! Very Rare Spawn.. Wow awesome ,i was so excited.
I mount up ,fly towards him ,noone was there. Good
I mount him & Start killing him ofc. & while i was nuking him ,he went flying around deepholm.
And so when i fnally kill him ,he drops down ,at some canyon near the edge.
And he missed to land on upper part & continued to fall down the edge.
& guess what happened... He landed somewhere in the middle ,where i couldn't Dismount/Land to loot him! Yea i couldn't loot him from either side ,up or down
So after a while trying from various positions ,his corpse finally Vanished & The Mount with him
/Applause for me. i know...

/FACEPALM.. Yea i'm still Facepalming Atm....Happened 3 hours ago.

(the link of what i'm talking about)
http://www.wowhead.com/npc=50062/aeonaxx