I would say DMT.
There are those theories about the pineal gland and dreaming and the connection between indigenous DMT, dreaming and the pineal gland.
IMO, DMT is very dreamy and when I return from my trip, I always have a very difficult time remembering exactly what happened. Just like a dream. If you don't think about it right afterwards, it becomes harder and harder to remember.
K-hole doses of ketamine would also be useful for what you are looking for.
I don't think deliriants are useful for much of anything.