The Jargon File (version 4.4.7, 29 Dec 2003):

bamf
 /bamf/

    1. [from X-Men comics; originally ?bampf?] interj. Notional sound made by a
    person or object teleporting in or out of the hearer's vicinity. Often used
    in virtual reality (esp. MUD) electronic fora when a character wishes
    to make a dramatic entrance or exit.

    2. The sound of magical transformation, used in virtual reality fora like
    MUDs.

    3. In MUD circles, ?bamf? is also used to refer to the act by which a MUD
    server sends a special notification to the MUD client to switch its
    connection to another server (?I'll set up the old site to just bamf people
    over to our new location.?).

    4. Used by MUDders on occasion in a more general sense related to sense 3,
    to refer to directing someone to another location or resource (?A user was
    asking about some technobabble so I bamfed them to http://www.catb.org/~esr
    /jargon/?.)


The Free On-line Dictionary of Computing (30 December 2018):

bamf

   /bamf/ 1. [Old X-Men comics] Notional sound made by a person
   or object teleporting in or out of the hearer's vicinity.
   Often used in virtual reality (especially MUD) electronic
   fora when a character wishes to make a dramatic entrance or
   exit.

   2. The sound of magical transformation, used in virtual
   reality fora.

   [Jargon File]