The rumors of Instagram spicing up Boomerang turned out to be true. It just introduced a host of creative tools, including an (arguably overdue) trimming feature. Much like the trim tool in your phone's video editor, you can decide just where the animation loop starts and stops -- no more re-recording a Boomerang or settling for a less-than-perfect endpoint. There are also three special effects, including SlowMo (half-speed playback), Echo (a motion blur trail effect) and Duo (a glitchy appearance).
As TechCrunch noted, these effects (like some of Instagram's features) aren't strictly new. Snapchat has had some of these effects since 2015, while TikTok has its own share of effects. However, they should give you a much better reason to use Boomerang if you're tired of the same canned animation in your posts and Stories.