Aerial Elephant is a KOTH minigame where players have to dodge the flying elephant to avoid being knocked off the platform.
Players spawn with plasma pistols and deal no damage (besides assassinations, but I can't turn those off in Halo 3). The only way to score is to survive longer than your opponents.
The elephant bounces off shield doors and launches off man cannons towards the platform the players are standing on. It can be a bit unpredictable at times because players can use the "flip" function on the elephant to change the direction it's rotating.
As PC file share is not yet added, to get this map, download the files posted and drag them into their respective folders in your game files.
For me it is:
D:\Program Files (x86)\Steam\steamapps\common\Halo The Master Chief Collection\halo3\map_variants
D:\Program Files (x86)\Steam\steamapps\common\Halo The Master Chief Collection\halo3\game_variants
OR put them into %userprofile%\AppData\LocalLow\MCC\LocalFiles
(starts at 8:57)