Traveling from Mongolia to Vietnam

Hello,

I'm traveling to Mongolia in September. I have no distinct restrictions on travel but I would love to make it to Vietnam. Initially i thought that to travel by train through China would be interesting however the more that i research it seems as if it may be easier to travel by plane out of Ulaanan Baatar. Thoughts would be lovely.

thanks!

Between any two cities 3000km apart, yes, it is easier to travel by plane. If you want easy, that's the way to go.
However, it is possible to go by train, and not really that difficult, just much much slower.
If you want to visit China and don't mind taking the train, you can do that. If you have interest in visiting China, or no time, then fly.