The Rabid Egg is shaped exactly like a rabbit found in Egg Hunt 2014. "Rabid" rabbit also refers to a crazy rabbit, as the egg's appearance suggests.
Go downwards on mountain where you begin, and if you have chosen the correct mountain, you will see a village filled with NPCs. In this village, there is a noticeable statue of the Rabid Rabbit. Near this, there is a red portal that you must go into; there, you will see his lair and you must defeat him to obtain the egg.
The hardest part about this is defeating the Rabid Rabbit, and making sure you have correctly found the village. However, the latter is not as difficult; this egg can be marked with a moderately hard difficulty.