Ayahuasca in a word
I have found that many people use the word Ayahuasca without real understanding of the word.
Ayahuasca is a word that really describes nothing, much like the word sandwich, I can ask you to eat a sandwich with me but you still do not know what you are eating.
Every Shaman brews their own brew with different plants. And every Shaman will tell you they are brewing Ayahuasca.
In South America many Shamans add things like tobacco juice to ensure vomiting and diarrhea, or "Toe" which is also known as "Devils Breath" which is not a hallucinogen, but a delerium.
What we call Ayahuasca is found all over the world all the way back to the Egyptians, made with many different plants.