I always thought it would be nice for Minecraft to have Hellhounds as either a mod or in the game normally. Hellhounds would be a new mob in the Nether. They have the same shape as the wolf but has a charred color to it and flowing lava in it's veins, it is only found in the nether and does twice as much damage as the wolf and has twice as much health as the wolf. The Hellhound can be tamed with Blaze rods and it can be healed by rotten flesh. The Hellhound basically acts like a wolf but it can swim in lava but not water. When attacking they could possibly set other mobs on fire with a 25% chance. The hellhound would be just as rare as the wolf in the Surface world.