It is not very difficult to make, but a bit of work.
Create 4 variables called up, down, left and right and create the following triggers (+ the similar triggers for left, right, down, upleft, upright, etc...)
press up trigger
player - player 1 presses the up arrow key
set up=1
trigger - run go up (ignoring conditions)
trigger - run go upRight (ignoring conditions)
trigger - run go upLeft (ignoring conditions)
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release up trigger
player - player 1 releases the up arrow key
if right equal to 1 then do trigger - run go right (ignoring conditions) else do nothing
if left equal to 1 then do trigger - run go left (ignoring conditions) else do nothing
set up=0
-----
go up trigger
events: (empty)
conditions: (empty)
actions: if up equal to 1 then do unit - order Knight 0000 to Move To Position of Knight 0000 offset by 10000.00 towards 90.00 degrees else do nothing
-----
stop trigger
time - every 0.01 seconds of game time
conditions: down equal to 0
left equal to 0
right equal to 0
up equal to 0
actions: unit - order knight 0000 to Stop
Good luck.
