It is the war between the Horde and the Alliance at the gates of the Undercity.
Anduin holds his sword up to the sky.
Light pours from the sky.
All of a sudden, it slams into Sylvanas.
She begins twitching.
As both forces look on, she pulls out a microphone.
She begins singing Jump Up, Superstar! (The theme song from Super Mario Odyssey.)
Everyone else begins singing along.
Everyone lives happily ever after.