Trader unlocks new sellables upon beating bosses. I think the eggs unlock after Moder or Yagluth.

I think it's the queen you have to kill

Originally posted by Nooberix:

I think it's the queen you have to kill

Queen does not unlock new items.

Then it must be yagluth. I killed it a few days ago to build some extra whisp fountains and the queen a few minutes ago. I never noticed the eggs from haldor before so I assumed it was the queen which unlocked it.

You have to kill yagluth to get eggs from the trader. If you had killed him before just put his updated drop in your inventory.