Character: dinky hooves
Dinky Hooves is a background foal who is very popular with the fandom. She is a unicorn filly with a lavender body (sometimes gray, to match Derpy), blonde hair and yellow eyes. She was first spotted in Episode 11: Winter Wrap-Up, singing along with the eponymous song.
Dinky is widely considered to be the daughter of Derpy Hooves, whether biological or adopted, and there is a great deal of fanart depicting them together. She is sometimes shown as the daughter of Dr Whooves as well.