Last minute I had a lightbulb moment and managed to finish this.

Now I think we all knew Spike was going to be Olaf. But why? Well, you see the main reason Olaf is in the movie is he's very cute and funny and happy. He is put on screen to make us smile. If you think about it, the main plot is actually very dark. A queen with magic ice powers that nearly killed her sister and runs away because she is afraid she'll hurt her loved ones and a princess trying to find and convince her to come back home to bring back the Summer. That alone could probably very upsetting for people and this is DISNEY so they need a character to lighting the mood and that's Olaf. Spike does the same thing. Every time he's on screen you can't help but smile.

P.S. I do not own my little pony or Frozen