For you game in Minecraft PE 0.12.1 and 0.11.1 has become very simple and you want to complicate the gameplay, then mod Extreme Herobrine Boss you will be definitely interesting. With it, you can add a very strong boss, a battle which will be really difficult and interesting. All the time he will be passive until you attack it, or at least not hit me once. For the battle with him it is advisable to wear the most solid, diamond armor and get more powerful weapons.
It is not recommended to call Cherubina in the dark and in the shroud, as the battle will almost always have one outcome, you will die. In addition, be very careful in battle, since he can teleport and can easily be behind your back. This modification will make the game Pocket Edition is really challenging and interesting.