Order of drawing:
    Sprite objects
    Bombs and projectile explosions
    High priority enemy projectiles
    Enemy layer 0
    Enemy layer 1
    Enemy layer 2
    Samus
    Projectiles
    Enemy layer 3
    Enemy layer 4
    Enemy layer 5
    Low priority enemy projectiles
    Enemy layer 6
    Enemy layer 7

After resolving sprite priority (i.e. discarding overlapping sprites of lower priority), they are then resolved with the backgrounds

Mode 9:
    BG3.1
    Sprites.3
    BG1.1
    BG2.1
    Sprites.2 (most Samus / projectile sprites)
    BG1.0
    BG2.0
    Sprites.1
    Sprites.0
    BG3.0
    Backdrop

.N is the per-tile priority bit