Zenlike Productions put Big Hero 6 (the visuals) together with Avengers: Age of Ultron (the audio) and put Baymax in the role of Ultron. When I first clicked to watch the mash-up I didn't really know what to expect. I was worried that they were going to put live-action elements into the animated elements.
But as the trailer went on, it became obvious that the mash-up was definitely working. I don't know how Zenlike Productions did it but they made Baymax, who is arguably one of the cuter/nicer/friendlier/etc. Disney characters seem like a huge villain. Maybe it was James Spader's voice and the editing, I don't know. But I definitely see Baymax in a different light now.
Also, I was really upset (by this I mean I wasn't and it was actually really clever) that they took one of the most emotionally draining moments of the film (when the older brother dies) and edited it in a such a way that made it seem like it was Baymax's doing. Geez, way to tug on the heartstrings guys.
Anyway, enjoy the mash-up above and let me know what you thought!