Dormant Shell Patch

This patch replaces the hopping green koopa troopa with a shell that never wakes up.

[Download] Green Paratroopa to Dormant Shell Patch

The hopping green koopa troopa is referenced in the disassembly as OBJ_PARATROOPAGREENHOP. These are recognizable from the middle of Level 1-1 where they are hopping down the colored blocks toward Mario.

Green Hopping Paratroopa

Green Hopping Paratroopa

After using this patch, this enemy spawns already in “shelled” form, and it will never wake up.

Patch Details

The source diff for this patch can be found on my branch for it on GitHub

The green hopping paratroopa is implemented in bank 4 (prg004.asm in the dissassembly). However, objects in the shelled state are handled completely by code in one of the fullest banks in the game: bank 0. Due to this, the code for singling out the green hopping paratroopa to never wake up is implemented in a bank that is always present in memory. This avoids switching banks within enemy handling code, which is one of the main causes of lag in the game.

I usually try to avoid putting code in the “always present” banks (prg030 and prg031), but there truly is a lot of space and this is one of the times I think it’s warranted.

To implement this patch, I modified the green paratroopa’s initialization routine to be a custom one I fit in some dead code in bank 4. The custom routine simply sets the object state to shelled rather than normal before calling the standard initialization routine.

	;;LDA #$10
	;;STA <Objects_YVel,X

	;;; [ORANGE] We removed the 4 bytes of dead code above to fit this small Init_Shelled
	;;; The JSR is only 3 bytes, so we have an extra $FF byte here to fill the 4 bytes we removed.
	.byte $FF
	JSR Object_SetShellState		; [ORANGE] This sets A to $FF and so returns zero flag not set
	BNE ObjInit_GroundTroop

Listing 1: Assembly for initializing the green paratroopa

This forces the green paratroopa to spawn in shelled state, but it then wakes up 255 frames later.

To handle this, we look at the code handling objects in shelled state in bank 0: the routine named ObjState_Shelled. Within this routine, Object_ShellDoWakeUp is called. This routine has some checks for specific objects, including OBJ_BOBOMBEXPLODE and OBJ_ICEBLOCK, and we insert a hook after those to check for our own object. Our hook is placed over top of the code that gets the wakeup timer to see if the object needs to wake up.

This allows us to check the object first, and then always set to the wakeup timer to be a high value prior to the game checking if the object needs to wake up.

	;;; [ORANGE] We can modify the wakeup timer here for specific objects
	;;;LDA Objects_Timer3,X
	JSR GetWakeupTimer

Listing 2: Assembly for disallowing our green paratroopa shell to wake up

Patch Application

This IPS patch can be applied via Lunar IPS.

It should be compatible with every other patch found on this site, but due to the complications involved in keeping many patches compatible with each other you may run into issues if you apply multiple patches.

The patch can be applied to either the US PRG0 or PRG1 versions of the ROM. Typically, if you have a ROM that isn’t labeled PRG0 or PRG1, it is PRG0. The PRG0 version of the ROM has the “better” world names during the credits after beating Bowser:

Grass LandGrass Land
Desert HillDesert Land
Ocean SideWater Land
Big IslandGiant Land
The SkySky Land
Iced LandIce Land
Pipe MazePipe Land
Castle of KoopaDark Land

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