Grouchy Pig are fluffy pigs that have big bushy eyebrows and yellow eyes with a green iris and black pupils, . They have a grumpy expression.
They are a parody of the Grinch, a humanoid monster that hates Christmas. He is a character from one of the stories made by Dr. Seuss.
On the Holiday Oink Tournament, if a player destroyed a Christmas Hat that a pig was wearing, the pig would transform into a Grouchy Pig, restoring the health of the defeated pig, the Grouchy Pigs are stronger and hard to defeat.
Grouchy Pig in the Holiday Oink Tournament Ad for Angry Birds Friends.