#68 Vampires could polymorph (+ some other possible limitations)

[Javier Fernandez-Sanguino Peña]

I think that a nice addition to the Vampire race, that
might not unbalance the game too much, would be to give
them an ability in order to polymorph into three
different creatures:

- a wolf
- a fog cloud
- a bat of vampire bat

Since the choice of polymorphing the vampires into is
limited it might be better to do it based on a
#technique that grants that ability once the vampires
get to higher levels

So maybe:

- A Vampire of lvl3 can polymorph into a vampire bat
- A Vampire of lvl7 can polymorph into a wolf
- A Vampire of lvl10 can polymorph into a fog cloud

It will be also nice to itnroduce other limitations or
consequences of being a vampire that might (or might
not, haven't checked):

- Vampires should not be able to cross running water
(even if flying)
- Vampires should not be able to cross into houses
unless invited, this affects houses in city levels, but
not shops. Thus, they should not be able to cross the
doorway even if they unlock/break the door to a house.
- Vampires (of a given level?) should be able to create
vampires if they kill with a bite a human creature

That's just to make a Vampire game more interesting, of
course, this is quite a lot of work to implement :-)