What is the best set up I can prepare to attract one,, thank you in advance,

You won't get a festive Unicorn until you open your present under tree until 25th December. It will be this years ready for harvest one.

Sorry, if you don't have rainbow rocks, maybe a mushroom black unicorn/ upwards, a poinsettia and vegetables is what I would recommend.

If you completed the pond the rainbow rocks are free which when a mushroom is planted makes it RFH IMMEDIATELY

I started one last year but finished it this year. Will it work?

To attract the Festive Unicorn, do the mushrooms have to be ready for harvest for the first one?

Alessandra no as long you are attracting it as in the mushroom above the pink cap (enchanted pink mushroom) and all the rest above it will also attract unicorn so you can use one of those but you of course will attract all that goes with that mushroom and lower myths as well.

Dana: No.  The Wildlife Guide specifically states it must be this year's tree.

I've put a pink cap in, but without rainbow rocks it won't be ready for five days.  Until it's RFH I'll probably get some myths on my plates, but once its rfh I can put out something to make it snow and high veg and just get festive (or elf) mice with a rare festive uni on the plates.

Or I could have put the one above the pink cap and then used high veg and got plates of mice (again could make them festive or elf type) along with dragons and pegasus. But this way the festive uni could come a lot sooner as the mushroom could be diamond dusted to fully grown on the same day as opening the present.

Any of the even higher mushroms would be the same scenario except for adding in occasional visits from other unicorns, and that could be fun, but it also could mean it takes longer for the festive uni to turn up.

I don't see a right or wrong answer to this.

There isn't a right or wrong answer :)