Or in other words, is it possible to pronounce [ʙ̰], [r̰], [ʀ̰], or [ʢ̰]?
I tried to pronounce these phones by myself, and I always failed. It seems the airstream from the constricted glottis cannot match the "sweet spot" to make the articulators trill.
On the other hand, pronouncing breathy trills is easy. I just need much airstream.
Yet, since my native language (Korean) doesn't have trills, I might be wrong and it might be the case that I just need practice. Is it really possible to pronounce creaky trills? If so, what languages do have them?