Not exactly a seed combination, but I think it would be neat if there were a certain set of specific features that you could enable from various secret seeds without having to enable the rest of the seed. Some of the more useful ones I was thinking of would be the option to generate both evils or both ore types from the same tier or default to otherworldly music when you load the world (from drunk seed), enabling the weapon progression switch (from don't dig up), or adding the rare items to princess's shop (from celebrationmk10).