If I'm remembering correctly, all of my experiences with entities have been facilitated by Psilocybe cubensis or Salvia divinorum. I've never had entity contact on anything like DMT (not yet at least?), 2C-E, 4-AcO-DMT, ketamine, LSD, etc.
I first met an entity once on a 1/4oz of cubensis. It looked like a constantly shapeshifting mountain made of all kinds of organic forms, like vines, plankton, eyes, people and mushrooms (of course), just standing there in my darkened bedroom transmitting all this nearly indecipherable information to me. Somehow it was very alien but also felt so very familiar, like remembering a part of me that I'd forgotten even existed. The entity felt like an embodiment of "the void," and by virtue of this just being in its presence caused me to experience something like what I imagine death is like.
On my last trip with P. cubensis (almost a year ago) I'd eaten an eighth at a particularly stressful time in my life where I felt overwhelmed and depressed by my circumstances. I was looking for some direction and needless to say I got it but it was by no means pleasant. Coming up I experienced an extremely disproportionate amplification of my everyday thought processes, which were quite neurotic at the time. About an hour after ingestion I was visited by two "minor" entities with a another, greater one some distance behind them observing and guiding what they were doing. And what they did was abduct me in the classic alien sense, in that I was being sucked into some fractal/between dimension and they were probing my chest/abdomen by sticking their arms in and feeling around, which was incredibly painful. Opening my eyes and pacing around brought me back to Earth somewhat but I still couldn't really think straight until T+8:00. I was left with the message that I had to change my living/work situations or I would go insane. I'm very grateful for the experience now but at the time it was very difficult to integrate, probably because of how blunt and direct they were with me.
With Salvia I've only felt a vague female presence in the background (or perhaps she was the background?) but encountered more explicitly some "minor" entities that were somehow working on behalf of her. The most vivid recollection I have of them is lying on my bed after smoking a good sized bowl of 5x and seeing a portal open in the fabric of reality just above my head. These entities appeared in the portal and caused the top of my head to open up, and were beckoning me to leave my body and go up there with them. I was almost there but then the trip started to fade after what felt like only 5 minutes but in actuality it had been about a half-hour.
BTW I'm using "entities" and "aliens" interchangeably here. And I tend to keep an agnostic attitude when interacting with these intelligences, i.e. whether they're coming from inside or outside of me is irrelevant and trying to figure it out just confuses things. They appear real enough at the time and more often than not have something important to say, so I just listen and separate the wheat from the chaff afterward.
Edit: I'd really like Propyl Power to weigh in here as he's said things about plant/chemical allies that I think could add to this thread.