Frozen 2: 8 Revelations From The First Trailer
3. Olaf And The Flaming Heart
One element that is noticeably absent from the majority of the trailer is Josh Gad's Olaf. The character only appears twice in the trailer and honestly, that's probably for the best.
His goofy energy doesn't immediately seem like a perfect fit for this somber trailer. And on top of that, it wasn't but just a year ago that audiences were openly recoiling and petitioning for the removal of Olaf's entirely-too-long short film, Olaf's Frozen Adventure, from in front of Coco's theatrical release. So if any of these characters could still use another moment away from the limelight, it's probably Olaf.
But one of the shots he does appear in sees he and Elsa trapped within some purple flames/smoke in the shape of a heart. It looks harmless enough at first but then Elsa starts blasting at it with her ice powers to no avail, making it clear that they are trapped within it.
Judging from the elemental designs featured in those crystals from earlier, this moment looks as if it could be an unseen character using heat-based powers against Elsa and Olaf.