OK, so my friend and I were up all night designing 5 new mobs. And here they are!
#1: The Giant Frog: The Giant Frog would, well be a giant frog. There would be two types, an evil type and a good type. The evil type could be like a marsh frog that will leave trails of glop which in potions could be used to make either a poison or a defense against the frog.The good type would be very rare and would be able to ride under water. They could only spawn during thunderstorms when lightning hits water. The trail of goop would be called frog goop.
#2: The Talking Trees: Talking Trees would just murmur in the background of forests, voices differing on the type of forest. However, the closer you got to a talking tree, the louder it gets. If you can find it, you can walk through the trunk and find a lot of treasure. When you got all the treasure, you could hit the tree and it would turn into the tree that that forest is made of. Talking Trees trunks are 2x2, so like a giant jungle or giant oak tree. They are very rare.
#3: Giant Birds: Giant Birds would be a little smaller that the Ender Dragon, but twice as fast. They are brown, black, white, or gray, but you can dye them like sheep. They are hostile, but only if you hurt them. If that happens, a flock of birds will attack your house, leaving it destroyed. However, if you give them apples or bacon, they will be your friend, probably nesting in a tree near your house or in a cave. If you build them a cave they will live in it. You can also ride them, but it's like training a horse. They breed like any other animals, find two and give them food. You can attract them by building a Bird Caller, which calls birds.
#4: Cave Trolls: Cave or Mountain Trolls are giant, smelly, stupid brutes that smash and destroy things in caves and mountains. They can only survive in darkness, so torches, glowstone, jack-o-lanters, sunlight, and lava destroy them, turning them into stone. They drop troll amulets, which you can craft into armor. The armor is useless against any other mob, but is the one thing that will protect you against trolls. Trolls live in packs of between 2 and 5. A troll home is not common and is like a temple, only underground. Trolls are either 3 or 4 blocks high, but their babies are only a block and a half high. If you can find a troll village, which will be in very big mountains, it looks like a regular village only really dark. Trolls make grunting noises, and shuffle their feet.
#5: Cyclops: Cyclops are very good mobs. They only have one eye, but are extremely intelligent. They forge in volcanoes, and there are generally 3-10 per volcano. They make diamond armor and will fight mobs. They have fire-proof villages inside the volcano, and there are women and children there too. They have rustic, medieval stores that have everything from apples to zombie heads. They will not hurt you, but just refuse to trade with you if you hit them. Cyclops are the most powerful good mobs that spawn.

Thanks fro reading, please tell me if you made these mobs into a mod, because I would like credit. Thanks, please diamond, fav, comment, enjoy!