Pets

Orders given to Pets:
Pets have been under-utilized in MMORPGs. I'm not sure why. Maybe they are a lot harder to effectively program than I imagine. Maybe friendly AI is harder than enemy AI. (and we all know that MMORPGs aren't the greatest at enemy AI.) However, I have a dream for 'pets' that extends far beyond a summonable wolf or skeleton.
Pets come in 4 distinct styles.

1. Summonable non-sentients: These are your elementals, and your 'mysticals' I'll call them. You can think of these as simply "Damage over Time" spells. You select a target, and the 'pet' appears and does it's job without input from you, and then disappears again. It could be they are attacking your target, or perhaps it's a beneficial 'pet' that hovers around you intercepting incoming missile attacks. Either way, it's not just a spell because it summons an entity that can be targeted, attacked, and killed. Often this entity will only have a limited life span anyway.
Possibilities for this class of pet would be poltergeists, fire or ice elementals, spirits, swarms of insects, packs of pixies, etc. There would only be a few simple commands that can be given, such as attack or defend and those commands would be inherent in the method the pet was summoned. These pets can't be healed.

2. Summonable/Trainable sentients: These are your typical MMORPG pets. These are animals or 'creatures' that you call up like a spell, but then give commands to. Or, these are wild creatures that you charm to be under your command. You take the pet with you through different encounters until it finally dies. Then you simple order up a new one and go on. These are basically the disposable variety of full pet.
Possibilities for this class of pet would be golems of all kinds, mundane animals, skeletons, and higher levels of ghosts. These would have all the typical commands, attack, defend, follow, stay, etc. These pets can be healed, but if they die, they are gone.

3. Permanent Pets: This is the main type of pet that MMORPGs should implement. This is an actual pet. It has a name. It stays with you. It's not just a random creature that you use and then get rid of. These pets would either be trained in a much more elaborate method than the temporary pets, or they would be purchased from others who did the training, (possibly NPCs.) They could also be NPC who you 'hire.' When these pets die, they go back to their spawn location. They can also be healed or resurrected.
Possibilities for this type of pet are mundane animals, NPCs, and friendly mobs. These pets have the whole gamut of commands. Everything that's come before, including some new features. They can be sent home, or they can come when you call. They have an inventory and equip slots appropriate for their type. They can be commanded to emote in different ways, and you can also put words into their mouth (for the types that should be able to speak.) Healing and resurrection spells work on them just as if they were another player character. These pets would also 'level up' to stay within the appropriate level of their master/owner.

4. Mounts: Pets that can be considered mounts are permanent pets that meet the right physiological profile. They have a name, they die and respawn, they can accept all the commands of the other pets (within reason), and they have an inventory and equipment slots. They are also big enough to carry the player, and are of the right stature. Once the player is mounted, they control the pet directly. When unmounted, they use the normal commands (follow, stay, etc.)
Possibilities for mounts are of course, horses, large wolves, gryphons, dragons, anything that can be mounted and ridden. Mounts for the most part would not have the 'speech' capabilities, and some mounts would not be able to attack or defend, because it's not in their nature or design. A mounts speed/abilities would increase as the owner leveled. Just like permanent pets, mounts would either be trained by the player, or they'd be purchased from dedicated trainer.

By merging pets and mounts we've given more capabilities to each class. We've also added the emote and speech capabilities that have been possible for pets since the early MUD days. Perhaps the biggest change we've made to the game feature is the permanence, where your pet will have a name, and will die and respawn as if they were another player. That adds very little in the way of complication programmatically, but it increases the attachment and emotional value of the pet immensely.