Gotterfunken is a green dragon boss.
Gotterfunken is a secret boss, found in a hidden room in one of the premade ice castles. (It is the one with the two high mountains. Gotterfunken is found inside of the mountains, about 60% of the way up. This same dungeon has another secret room with another secret boss, Shelob.)
He has two attacks. The first one is a fireball, a projectile that sets you on fire if it hits. The second is a charge, similar to the attack of the Naga from the Twilight Forest mod. In addition to these two attacks, he may fly into the air. Because the room is relatively small, this is not too much of a problem.
Gotterfunken has 400 health, and regenerates 1 health every few seconds.
Gotterfunken can also be ridden by a walker king if they are in close vicinity. It is unknown if this is the case with other boss mobs as well.
Tips for finding Gotterfunken:
1. He only spawns in the premade ice castle with 2 mountains.
2. He is in the mountain to the right of the skull on the ground. In the path at ground level between the two mountains, there is a skull facing a particular direction. To the right of the direction the skull is facing is the mountain that contains Gotterfunken.
3. He is in the bulk of the mountain, in a medium sized hollow room about 60% of the way up in terms of height. This is around level 106, or about 15 blocks above the bridge between the mountains.
4. The wall of this room is only one block thick on the side that leads to the pass between the mountains. This makes it easy to go in between the mountains and dig around to find him fairly easily.
The Dragon Helmet and 10 diamonds