Valkyrie: Similar to Chrysalis in build in size, they lack eyesight. Their eyes have devolved to just fulfilling the purpose of light detection. Instead, they see the world through magic pulses, similar to sonar. Thus, they have larger ears to pick up the minute magical energies and sounds around them. They are the brains of the changelings, only taking orders from their queen. Thus, they fulfil the changeling equivalents of generals, supervisors and such. They also don't speak since they lack vocal cords, instead they rely on telepathy, which can be broadcasted to any being they so wish on the planet. (They are extremely strong in this regard, able to kill several beings with a Psychic screech.) Their magic is developed to another level, giving them spell maneuverability that no mere unicorn can match.
Soldier: These changelings are the backbone of the army. They are much larger than normal drones. Their spear like horns can pierce the hardest armor and can be detached if so need be. (It doesnt take much energy to grow it back.) They are also extremely strong, able to tear apart ponies, or any other creature with their bear hooves and lift objects several times their weight. They are known for their bloodlust. For once they catch the scent of blood they go wild, killing and tearing any being that so much come across them. Only the Valkyrie and the Queen herself can reel them in. They are reluctant to change their form, and will not do so unless instructed by a higher caste. They have a massive healing factor, linked to how much love they contain and strong the changeling is. They can survive wounds that would be fatal on any other creature, are extremely sturdy, and can even regrow limbs within in seconds. (That last one only goes for well-fed soldiers, since that taxes on their energy reserves.) Their wings, which have taken a more draconic shape, can act as impenetrable shields, since the material they are made of is impervious to both magic and mundane weapons. {it also makes for a cool cloak when not being use.}
Nurse: The most beautiful of all changeling castes. Their role is to take care of the young and the wounded. As such, they are guarded well and kept far from enemy positions and areas deemed dangerous. They are gentle and loving creatures. (Imagine Fluttershy as a changeling.) They will not harm any other being, except in extremely dire situations. Instead they use two methods of preservation. 1: A piercing shriek. Which also alerts other changelings of an intruder.
2: Pheromones. The Nurse caste can release pheromones upon any creature, putting it into a more calm and blissful mood and allowing them to be easily swayed. This is not effective against large groups.
Their saliva has extreme healing abilities and can cure any illness as well as seal any wound within minutes.
Swimmers: These changelings are a breed of changelings that have taken to the water. They are known for their tantalizing voices, luring ships to their doom so they may feed on their occupants. The seas are often red by the time theyre done.