Moving Tile based "Background Boss"


How do they do it? There's some specifics with Ninja Gaiden, as they have a HUD, and "Floor", I'm mostly looking for a way to control the BG tiles in a controlled way (Up/down, left/right) without freaking everything out.

I managed to create something that will scroll forever in 1 direction while leaving the player control, but can't figure out how to "stop" it in a controlled way, or reverse it (Perhaps need 4 controls, 1 for each direction, that can be told to loop X times, then stop??) I don't know enough about these calls to figure it out myself, so hoping to source the hive mind. If you have any insight, appreciated!

Code:
    LDA UpDown
    CMP #$01
    BNE NotFinalBossScreen


    movement:
    INC yScroll
    INC XScrollNo

    LDX #20
    CMP XScrollNo

    BEQ moveBack
    JMP movement
    ;RTS

    moveBack:

    DEC yScroll
    LDA #01
    STA UpDown
 
Have you tried attaching your script for scrolling to monster actions? (not end actions). Basically have a blank monster that can move screen left/right/etc with each action as it cycles through its actions. Might be a good place to start.
 
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I have a more working model after Joe's recent video about the boss phases. It was going to be a "Falling through the sky" sort of boss, but the top and bottom bounds are causing me massive headaches, so maybe it'll be on a single plane like shown here.
 
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