If you could bring one mythical creature to life, which one would it be?

And introduce an invasive species into our present environment? . . . Perish the thought.

I would have to bring a whole mythological ecosystem just to have the checks and balances in place so as not to have some sort of new Apex Predator . . .

I guess a single Pegasus couldn't hurt . . . . As long as it couldn't reproduce. 

House Elves!  I could use the help with cleaning.  It gets in the way of playtime.  :)

Two unicorns---male and female, and modified if necessary so that they have no natural predators (including warped humans).

(I would have to make numerous other conditions extant to provide for their presence.  It now occurs to me at the moment that being God is much more difficult that just having ultimate powers---there are so many ancillary considerations when you create interdependent creatures.)

Pegasus.  Think of all the traffic I would avoid and the great places I could see!

A sorcerer. I'd pay him as an assistant.

No ecological impact, nobody even need know.

All of my favorites I wouldn't be able to appreciate unless I had the option to turn into them