Whether this is a taur-like species that is good at all ground terrain, a bird species that can transport you across impossible to walk terrain, or a mermaid/other sea creature that can take you to secret underwater locations or island/continent hopping. The only unforeseen problems, even if they have every intention of letting you go on the other side, is the distance involved and the time it takes to get to the destination. So depending on which transport method you take they each have different digestion strengths/speeds, and if there any possible delays like bad weather or detours required then you run the risk of staying inside their stomach too long and you're mush before you've reached your destination(scat)
Spoiler: show