For me they should be about as thick as a penis or slightly thicker. They should have a penis head or similar for the tip, and should be impossibly strong. The best colours are black, purple and red, but green is fine too.
My favourite thing for tentacles to do is easily to first, to grab and bind the girls male companion, probably boyfriend, and force him to watch what's about to happen. Then, grab the girl's ankles and pull them apart, rip all her clothes off, and then, while she's standing, with no foreplay, instantly start fucking her vagina. As she squeals in surprise, she gets one in her mouth.
She's still standing on her own two feet, possibly pulling in vain at the tentacles with her hands.
After 30 seconds or so, one softly pokes at her asshole, and as she moans around the tentacle in her mouth and tries to shake the tentacle away by moving her hips, and moves hers hands to cover her butthole, but too late before it forces its way in.
Finally the cumshot - it's difficult for a hentai animation to show what I want properly because hentai nearly always goes for opaque white cum, which is hot, but I'd like a translucent white cum, which she gets not only completely filled with, but completely doused in as well by all the other tentacles that the monster has that weren't doing anything, but just getting ready for ejaculation. This way she can be totally covered but we can still see her naked rude bits, she isn't just a white blob.
Instead of the classic yet nearly impossible torrent of sperm that explodes around the penetrating tentacles in a creampie, there should just be the sound of liquid filling her, like some kind of pump action, and of course her swallowing noise in between moans as she is forced to swallow it.
Then, as the tentacles exit her body, she starts coughing, and tears well up in her eyes, not through pain but simply because she's having a coughing fit. As soon as the tentacle leaves her vagina, all the tentacle sperm floods out down her thighs and onto the floor in a small puddle. She falls onto hands and knees and the tentacles on her ankles let go, and she mumbles "no... no... no... don't watch...", while very slowly attempting to crawl forward, and then squeals as she loses control over her anal sphincter and she spews cum from her ass. In the mididle of this she loses the last of her energy and collapses in the puddle of cum, and her boyfriend is released and runs to the aid of his embarassed and shaking lover as the last of the cum leaks out of her orifices.
...sorry, what were we talking about again?
