Quite an odd OpCode. Used in an if check to see if an object is at an angle(1) and if it isn't, rotates it towards that angle by angle(2) each time it is called. Generally used as a NOT OpCode (834d), not sure what the effects of using 034d are.
Alex "Y_Less" Cole
834D: NOT object (object) at_angle (angle) then instant_rotate_by_angle (angle) (flags)