I have an idea for the greatest bad guy in MLP:FIM.
More psychotic than Discord, more heartless than Queen Chrysalis, more scarier than Nightmare Moon and King Sombra, and more violent, powerful, and dangerous than all of them put together.Goblins are a race of humanoid-like creatures with rough light green or gold skin, sharp teeth, and pointy noses and ears. Regular goblins are about pony-sized, but hobgoblins (a different kind of goblin) are twice their size (about Princess Celestia's height). Few goblins are also able to do Magic. They are not known for being the friendliest of creatures, but they are known for being the cleverest. Goblins have been lurking in the darkest regions of Equestria, and hasn't been seen by anypony for a long time.
One day, one hobgoblin named Malice decided to leave the shadows, and terrorize Equestria for kicks. A ruthless hunter who has gone mad with power, hunting and battling the mightiest creatures in Equestria to satisfy himself. He then turn his attention at the ponies.
Malice is obsessed with the thrill of the hunt and the chase. He cares not for the princesses, the throne, or all of Equestia, all he cares is hurting others and find a "worthy prey". He is very clever, cunning, and careful. He would hide away and watch his prey thoroughly, studying their habits and weaknesses. Then he would wait for the right moment to strike.
He's a sadist. He finds pleasure in inflicting pain of others. Malice is cruel, merciless, and hostile. He hold no alliance to anyone but himself, not even to his own kind. He is only interested in good sport, and not in more powers, such as conquering Equestria. He sees ponies as weak and inferior creatures. So he hopes to find a pony who is worthy of his skills.
If you think Malice was a little too much, than maybe this version of the Ultimate Evil is better.
Vandal, Hunter, MonsterGoblin Ponies are a darker breed of ponies, like the changelings. This version of Malice shared some abilities, personality traits, and features of his humanoid counterpart: with the red eyes, pointy ears, and that yucky green skin; with two horns instead of one; sharp claw-like hoof toes; and arm-like appendages with a special organic fabric-like translucent to help him glide.
Malice is an unstoppable psychotic force of destruction, destorying everything in his path. Burning down towns and hospitalizing ponies, all to satisfy his own twisted pleasure.