Quite honestly, I think the abilities sound good. The part about 'parasitic appendages' is a little unclear to me, but it should be understandable in the context of the story. From how I've understood those abilities, it would be most interesting to have the main character/parasite take on a supportive role in a group, similar to a buffing/debuffing class in video games. 

Building a story around that would be very unique and thrilling in my opinion, but I don't want to limit your creative freedom. Just start up a story, and if you don't like it, scrap it or remake it. There's no shame in trying more than once!

I get that, but I can't seem to stick to an idea or really do much with anything I do stick with. I'll keep on trying but nothing I make is good enough or even something I would want out there right now. I appreciate the talk though. Have a good one!

I'm not sure what you mean by that, but if you got any ideas you want to share, just leave them here and I'll tell you what I think about them. My own story sadly isn't really about parasites but more of a typical LitRPG trope, so I can't give too much advice. However, I'd say just pick one and start writing whatever you want. You can still flesh out the full story later on, as long as you don't go too crazy in the first few chapters.