It's the awesome thing you didn't even know you desperately needed. Dr. Horrible himself, Neil Patrick Harris, guest stars in a special episode of Adventure Time next Monday — and now the show is Adventure Time with Fionna and Cake!

Here's what Cartoon Network told us:

Neil Patrick Harris stars as Prince Gumball in "Adventure Time with Fionna and Cake", a gender-swapping, parallel universe episode featuring the female "Fionna" and her cat "Cake."

And Prince Gumball sings an ode to Fionna, as you can see in the above clip!

Also, here are some pictures:

How much do we love this show? Adventure Time airs Monday at 8.