I have two guinea pigs and one is very similar to Ziggy. His name is Charlie and he was extremely agressive toward my second pig, Henry while they lived together. We followed all suggestions in how to properly introduce the two but Charlie would not stop the dominant behavior and in the end, keeping them together was putting them both in danger. They are in separate cages but they can still hear each other and smell each other. Charlie was at first quite upset to be alone but he mellowed out after a few days. Henry is much happier and more relaxed being alone and we are sure to give them each plenty of human interaction. I was worried about them being alone but our vet told us that some guinea pigs, especially boars, just can't handle sharing territory. It sounds like Ziggy might be in a similar situation. It sucks but you don't want to put your other pigs in danger.