My favorite thing about tentacles is the stretch of the very big ones/multiple ones in the same hole and when there are many tentacles involved filling every possible orifice. They should be fucking, deep-throating, and sounding him, all at the same time, possibly while also holding down his arms and legs so that he can't move. Ooh, and maybe wrapped around his throat? I love oviposition too, but honestly mainly for the added extra, impossibly big stretching.

I'm good with human or monster from the deep, but I generally prefer a little creepiness and dub-con involved over complete consentacles, at least initially. And I really, really love if someone else is witnessing it and can't/doesn't want to stop it.

...basically, tentacles give me the possibility to hit my bondage, extreme penetration, humiliation, and dub-con kinks, all at the same time!