I figured it'd be better to organize all the mob suggestions into one area to reference for future use! Like what was done for the list of spell suggestions.
Guardian-goyles
Featured in episode 21 of season 9, Daring Doubt
Spawns in temples
They are a statue/block that transforms into a hostile mob, I was thinking the trigger could be when you loot the temple as per the show?
Could potentially drop a "bring to life" spell like what Twilight casts in Winter Wrap-up if that gets implemented
More likely drops sandstone (or other blocks depending on what type of temple you're in) and some typical temple loot like gold or enchanted books.
Winterchillas/Winterzillas
Featured in the holiday special Best Gift Ever
Adorable little passive mobs in the day, they transform into the hostile mob Winterzilla at night.
Probably spawns in various snowy biomes, most likely frozen peaks, grove, and snowy slopes biomes in particular. The snowy taiga biome might be nice, but I worry the Winterzilla model would be too big for as many trees are in the biome. The grove biome might also be pushing it a bit, but I do so enjoy the vision of the winterchillas running around a foresty area like foxes do.
Possibly drop wool, or some variant of it? I could also see bones as a drop for the Winterzilla form specifically.
Whirling Mungtooth
Featured in episode 22 of season 9, Growing Up is Hard to Do
Spawns in swamp and mangrove biomes.
A tameable passive mob, probably does smaller idle tornados every once in awhile that can hurt if you're too close to it
When attacked, turns into a bigger tornado to suck you toward them and hit on impact when in a certain proximity of it
Damages you in tornado mode the way a cactus does?
Timberwolves
Unlike wolves, they are NOT tameable and are hostile mobs
Spawn in dark forest and (depending on how it is decided to implement it) the everfree biomes.
Can be knocked to pieces with enough damage or with an earth pony's ground pound, as we see Applejack do similarly in the episode Spike at Your Service.
Comes back at least once after being "killed"/knocked to pieces, at maximum can come back three times before being killed permanently, as seen multiple times in canon, but most prominently in Spike at Your Service.
A somewhat rare spawn due to their high difficulty to fight (however with how powerful I feel the ponies can become with their abilities, this can be increased to a higher spawn rate upon testing.)
Sirens
Featured in the film Equestria Girls: Rainbow Rocks, as well as the 26th episode of season 7, Shadow Play - Part 2
Likely spawn in ocean biomes, as well as the cliffs and beaches bordering them.
Could potentially have variants that spawn in other dimensions to reference the banishment of the Dazzlings? I'd imagine these would be more powerful bosses rather than regular mobs though, which might as well be the Dazzlings themselves.
Can swim through the water as well as "fly"/swim through the air to follow you on land or sky. Unicorns likely have the best chance of escaping them using teleportation.
Has a significant amount of health, your best bet of defeating them being to damage the gemstone in the center of their chest and rendering them unable to attack and significantly weakened.
Alternatively, you can only damage them by attacking the gemstone in their chest. Can use this or the suggestion above depending on what feels better in testing.
Has a sonic scream attack (not unlike bat ponies) based on the one in Rainbow Rocks
Has another method of attack by summoning hostile mobs to defend them or turning nearby passive mobs hostile toward you. Can make nearby players temporarily attack each other in multiplayer.
Could drop fragments of their gemstones to be crafted into a whole one, which can then be used to take advantage of their sonic screech or brainwashing ability.
Ursa Minor and Ursa Major
Featured in episode 6 of season 1, Boast Busters
Both spawn in various cave biomes, excluding the deep dark.
Usually asleep, they don't aggro on the player unless you make noise and wake them up, works similarly to how the Warden's ability to hear does, however they can just see you normally once they're awake.
Not intended to be fought directly and more to be tricked and out-maneuvered if you do awaken them, or encounter them already awoken. However, they can be beaten, and they are weaker than the Warden.
Umbrum
Featured in issues number 34-37 of the IDW comics, Siege of the Crystal Empire
Spawns in the deep dark, and perhaps very rarely in places with the lowest light value/absolutely zero light source.
Could potentially be added to the King Sombra boss fight as mini-enemies/summoned foes?
I could also see them spawning in the event of a crystal heart being broken, as extra incentive to protect it.
The crystal heart prevents them from spawning in a certain block radius, which I'll leave up to developer interpretation since I can't think of a specific number myself.
Perhaps they take on their innocent disguise until you get within range for them to aggro on you?
Orthros
Featured in episode 22 of season 4, Trade Ya!
Basically just cooler wolves, however they do extra attack damage thanks to their extra head.
Potentially only obtainable through villager trading as a reference to how it's obtained in the episode?
Diamond Dogs
Featured in episode 19 of season 1, A Dog and Pony Show, as well as issue 89 of the "season 10" comics.
Spawn in caves, perhaps in structures that somewhat resemble a very small underground village build into the cave walls?
Behave similarly to villagers, trading various kinds of loot in exchange for various ores.
If you loot any of the chests in their structure or mine any of the ores in their cave, they will immediately become hostile.
I'll be adding more over time, so feel free to check back periodically and add any suggestions of your own!
If you feed them apples, they can drop other kinds of apple seeds or seeds for apple trees that produce more apples, as Fluttershy comments in the episode that the seeds they spit out of the apples they eat produces stronger better apple trees.
If you do not either feed them apples to sate them and dissuade them from eating out of your orchards or kill them/chase them off, they will eat the apples in the area and drop rotten apples. Meant to reference their pest-like behavior toward Applejack's orchard, and the solutions that were proposed.
Commonly spawn in Sweet Apple Acres biomes like their cuter cousins below.
Utilize the pegasus model with Mine Little Pony installed, but otherwise resemble vanilla villagers with the addition of wings.
Spawns in a village form of cloud structure, but you'll occasionally find a few in a regular village.
Function like regular villagers, although they tend to trade uniquely pegasus/weather-adjacent items on top of the normal loot table, such as their feathers and weather jars as well as snow.
AI allows them to fly, and their code disincentivizes them from getting too far from the village to prevent them from jumping to their deaths on purpose. If fallen, will activate flight to catch themselves and seek out the nearest cloud block to land upon.
Utilize the bat pony model with Mine Little Pony installed, but otherwise resemble vanilla villagers with the addition of bat wings.
Spawns in village structures in the dark forest and/or everfree biomes, as well as potentially caves?
Function like regular villagers, although they tend to trade uniquely bat pony-related items on top of the normal loot table, such as unique fruits, sunglasses, perhaps even special variants of sunglasses such as rose-tinted/heart-shaped sunglasses, and bottles of blood.
AI allows them to fly, although they don't fly too far from their village. Will occasionally be found hanging from the ceiling, and only sleep during the day.
To protect themselves, their AI is far more aggressive toward hostile mobs than the average villager. Can and will defend themselves without the use of golems. This includes defending themselves from the player, so be wary about making an enemy. Especially since they're canonically known in the official novels for going head to head with dragons.
Perhaps lessen fall damage, just to be safe? Don't want them dropping to their deaths mid-flight, haha.
Utilize the unicorn model with Mine Little Pony installed, but otherwise resemble vanilla villagers with the addition of... Uhhh... Actually, unicorn players don't have horns without MineLP installed, do they? I suppose just texture them with fancy sparkly wizard outfits I guess?
Spawn in regular villages mixed with other types of villagers, but sometimes spawn in grander "city-esque" structures with a higher frequency of those villagers being unicorns.
Function like regular villagers, although they tend to trade uniquely magical items on top of the normal loot table. Important ingredients, the occasional gemstone, a staff, things like that.
Teleport away or blast you with spells if you attack them.
Have the chance to catch a changeling while transformed and despell their disguise. If caught, will attack on sight.
I figured it'd be better to organize all the mob suggestions into one area to reference for future use! Like what was done for the list of spell suggestions.
Guardian-goyles
Winterchillas/Winterzillas
Whirling Mungtooth
Timberwolves
Sirens
Ursa Minor and Ursa Major
Umbrum
Orthros
Diamond Dogs
I'll be adding more over time, so feel free to check back periodically and add any suggestions of your own!