Something bad.
Not really threatening coming from just a pegasus.
Excuse me, hornhead?
You heard me right.
What is a single pegasus going to do against a unicorn?
Apart from getting brutally beaten?
((You seem to underestimate pegasi))
Twilight clearly proved that pegasi can’t defend against magic.
((Yes, Twilight, probably the most powerful Unicorn in canon Equestria. No other ponies were shown floating another pony etc.))