Manual:DIL Manual findrndunit()

unitptr findrndunit( u : unitptr, sv : integer, uf : integer)
   Returns: A pointer to a random unit, or null
   u  : The unit pointer which the search is relative to.
   sv : The search-location, a value (not bit vector) of FIND_UNIT_XXX
   uf : Bit vector. The unit flags which can match of UNIT_ST_XXX

   Example: u := findrndunit(self, FIND_UNIT_ZONE, UNIT_ST_PC|UNIT_ST_NPC);

   This routine returns a random unit. Notice how the 'uf' lets you
   specify exactly what unit types to look for. The 'sv' is not a
   bit vector, although FIND_UNIT_XXX is usually used as such. If
   you need to search multiple environments, then call the routine
   once for each.

   Using FIND_UNIT_PAY or FIND_UNIT_NOPAY in this function will
   pick a random player which in addition to being in the search
   environment also is registered as valid payer (or not). Asking
   for a room would yield a random room registered to be accessible
   for paying players only (or not). Asking for objects would
   return no unit (null).