"Bigly" was once an accepted adverbial of "big" in English, but it fell out of usage over time and now is largely seen as nonstandard. Still, Trump's use of it (allegedly) could be reviving it...
Bigly is great! I love using it myself. I admit that Trump turned me on to it. It's a real world, but it's also a silly word. It makes me laugh. There was a lot of debate on whether he was saying "bigly" or "big-league", but I think he liked to say both of them. Sometimes "bigly" was obvious, and at other times it was obviously "big-league". But I prefer bigly better.