Minecon Earth Mobs Addon for Minecraft PE adds new mobs into your world. I think you already heart about Mojang vote. ( if not, you can see this video ) You can vote for one of the four mobs. Creator this addon, already realized all mentioned mobs in this addon. You have to just download and install it.
Which mobs you will see
The first one is Titan Squid
If you want to meet him, you have to try to find him under the water. He is incredible powerful and dangerous.
He looks like a Steve and he is hostile to you. The most dangerous ability is summon his mutants.
One more mob, whoch lives only under the water. Hostile to you. He can make you blind.
The last one Blaze King
Replaced by Witch
for Minecraft Pocket Edition 1.2 +