With the current level of technology, this is impossible. If you count people with some kinds of genetic disorders as "monsters" then a change in the genetic code is all that is needed. As for an already-living human turning into something like a dragon, this continues to be pure fantasy The closest that someone can get would probably involve a bionic exoskeleton (something likely to be developed considering the rate of technological advancement) covered with a flesh-like material and colored to look real.
apes
Shapeshifter are humans that can transform into animals, plants, and other humans.
digimon
well it kinda depends...what kind of transformation.??
Cookie monsters -and me!Humans
Vampires generally bite to feed on or to transform humans.
Monsters sleep when they are tired from hunting humans and need rest for the next day of hunting them.
Greek monsters were truly monsters that humans feared. They were large and had animal parts. Some were also part gods.
Ask Sunkaze on moshi monsters she has some
Only people with mental issues who imagine monsters having sexual intercourse with them.
Humans can not transform into wolves via magic spells. Though there have been many stories of humans transforming into various animals over the centuries, it is folk lore only and a physical impossibility.
Humans