Derpy asked me to forward this letter to everypony and that she’s sorry she hasn’t appeared much in season 3:
 
“””  
Dear my friends in Ponyville,
 
It’s been a while since I’ve seen  
everypony. Don’t worry though, I’m fine!  
The Doctor <3 and I have been time  
travelling a lot lately in his blue box that  
is smaller on the outside! We’ve been so  
busy saving Equestria (and other places too)  
from daleks, cyber ponies, and underwater  
tiger ninjas that I guess I forgot to  
stop and say hi… Last week we went to Victorian  
Angle Land and stopped some scary snowponies  
from space from eating these hairless pink  
monkeys called “hyumins”, just in time for  
the holidays too! I hope everypony got lots  
of muffins for Hearth’s Warming!
 
Your pony pal,  
Derpy Hooves
 
P.S. Go bronies! Woohoo!!  
“””