The animation frame index mask for a guardian is found
in bits 5-7 of byte 1 of its buffer (see 8100) while it is on-screen, having
been copied there from the corresponding entity
definition (see A000). The mask determines the animation frames that the
guardian's sprite cycles through. If 'B' is the guardian's base frame (0-7),
then its sprite will cycle through animation frames as follows, where '|'
denotes a bitwise 'OR' operation (see 9211):
For example, if a guardian's base frame is 2 and its animation frame index mask
is 011, then its sprite will cycle through frames 2, 2|1, 2|2 and 2|3 (i.e.
frames 2 and 3).
Note that the animation frame masks 100, 101 and 110 are not used by any
guardians in the game, and no guardian has a base frame of 7.
A guardian, arrow or rope.
One of the 128 8-byte blocks located at A000 onwards. Each one defines the
location and movement characteristics of a guardian, arrow or rope.
One of the eight pairs of bytes at the end of a room definition (e.g. at
D0F0). Each one specifies a guardian, arrow or rope present in the room.
An inhabitant of a room that continuously moves left and right (horizontal
guardian) or up and down (vertical guardian) in a straight line, or
stays still. Contact with a guardian is fatal. Some