Phase Creeper (sorry for bad pic)
A Phase Creeper is one of the most evil things that wizards did to native Minecraftian life. They realized that creepers were one of the most dangerous beings, so they wanted to make them even worse. One thing they did was create roflcondas, many creeper heads strung together as a living device of destruction and death, but they also created phase creepers. Not appearing until they are close to their victims, they are extremely dangerous and should be avoided or only fought by skilled heroes.
The Phase Creeper is similar to the original except for its ability to phase in and out of visibility. When you're lucky enough to meet one of these, stay back, unless you are at a decent level or at least a higher level than it. Even though a single Phase Creeper isn't much of a threat (much like the Roflconda), when in a group or charged, the Phase Creeper could over-power a less experienced player. Or simply a player with low health or no armor. Rangers are the best for dealing with these since they have some range, but can also fight in CQB situations. Phase Creepers are fairly rare, and are even rarer to be in groups. Lightning can be used to combat it's abilty. You have to be careful, for obvious reasons. Phase Creepers are thought to be found in most biomes of the world (mainly in plains as seen above).