Anyone knows Rainbow Dash loves a good race. Frost Quill is no stranger to that competetive nature having pegasus existing in his family line. Thanks to a spell he has that lets him have wings for an hour tops, he can experience a good race and give Dash some fun competition.

No, Frost is not an alicorn. He is a unicorn with a spell that lets him have pegasus wings.

Frost Quill © MikeArctic
Rainbow Dash and MLP:FiM © Hasbro Studios

[edit] added their cutie marks