In some settings bulettes hate the taste of elves, and maybe that could allow militaristic elves to domesticate them for use as raiding mounts. I'm imagining an elven archer atop a saddle with a bulette-hide shield along the dorsal fin. The shield is sturdy enough that it allows the rider to duck down and be protected while the mount tunnels, as well as providing cover when shooting their bows. I think this could work well for a single scout ambush encounter at level 5+, and as a special siege unit that the party has to defeat later on.
Maybe they learn about it from a group of wounded soldiers recounting a recent battle where a castle wall collapsed without warning, and in the chaos three mounted land sharks tore through their ranks until they were ordered to retreat.
The research lead me to an opposing conclusion unfortunately. tiktok+viral+heating in your search engine of choice shows results like these.