Notch revealed a screenshot of one of the new monsters for 1.8!
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Seen here is a screenshot of a new monster in the works for 1.8. While Notch didn't specify exactly what it was, it seems fairly apparent that this new arrival in Minecraft isn't especially friendly-looking. What is it? What can it do? We will keep you updated as this information becomes available!
Update - Thanks to Nyanners and KSMF, respectively, for the following two enhanced images!
Aside from zombie pigmen, living pigmen have been confirmed to appear in a future update.
In the Halloween update, Notch said he would add fish.[citation needed] However, he had limited time, and was thus only able to add them as an item. There is coding for fish in the game, but no model exists at this moment.
Dragons - Notch hinted during the Spider-Jockey update that he will add Dragons to the game. Dragons may also be able to fly or breathe fire. Notch confirmed on his Twitter that he will definitely add a form of flying transportation. There is a chance that Dragons may be able to be ridden in a similar manner to pigs.[3]
Notch confirmed during the Brocraft.net stream that he will be adding prefix mobs. This means that there will be mobs such as 'Burning Spider' 'Giant Zombie' 'Cobble Creeper', etc. It is not known if these are still planned to be in a future update.
A "scary monster" is planned to appear in the 1.8 update.
A new mob texture was found with Beta 1.7, titled silverfish. This mob may be one and the same with the "scary mob" mentioned above.
Jeb recently posted that he likes the idea of players deciding when to summon the boss mobs like in Terraria, which means that boss mobs may be added in 1.8.[4] Notch recently said something similar in an interview.
Notch said he was working on a new mob after drinking some coffee. This mob was shown a few days later, called an Enderman.[5]
Heres a small reference
Dragons,pigman (not zombies), fish, silverfish
After looking on minecraft wiki they seem to be a planned mob, they will damage wooden planks and paper based products
(i know this is off topic, but it's still related to new mobs)