I've heard of lot of stories like that. There are a lot in the Pali Canon and in Tibetan Buddhism. Tibetan Buddhism even has offering litany for such beings.
A Thai friend told me a story from his temple. Back in Thailand, a man dressed only in a sarong walked into a temple and without speaking, lit a candle, prostrated to a Buddha statue a few times, and then wordlessly left. Since this was so odd, a monk followed him and according to the monk, the strange man walked to a nearby river and went behind a large rock by the river. When the monk came behind the rock, the man had disappeared. So, the man was likely a Naga, a water spirit.
"All memories and thoughts are the union of emptiness and knowing, the Mind.
Without attachment, self-liberating, like a snake in a knot.
Through the qualities of meditating in that way,
Mental obscurations are purified and the dharmakaya is attained."
-Ra Lotsawa, All-pervading Melodious Drumbeats
"You must experience that the various thoughts, in whatever form they arise, are an empty appearance and not a definable entity."
-Clarifying the Natural State pg. 33