I have no idea what to base the (pony) song on and only have an acoustic guitar. :P
You may want to be a tad more specific with this request, some more details would be useful like, What type of song, A brand new song with new lyrics, a Cover? Are you writing Lyrics if it's a new one or do you want help creating a brand new song and have a tune, or using an existing tune and switching up the song?
I mean I have been working on a project like this myself well sort of for myself I'm only writing lyrics for a song since I can't make music but yea. A bit more detail and then I'll be able to help out more
Brand new one whole new melody, as for your project, maybe I can help
Ok then if it's a brand new melody what would you like it to say or mean, what emotion or feeling do you want and what is it going to be based on? (wow do I think way to much into these things) and as for my project thank you for the offer but I do already have plans for it, now for me it's time and planing (I've backburned a lot of projects recently)
Maybe a... happy/sad song, isn't there such thing?