Action

An action is a particular state that Mario can be in. Long jumping, crouching, and walking are examples of actions. Each action has code controlling high-level behavior such as Mario's movement while in the action, as well as transitions to other actions. Mario can only be in one action at a time.

It is likely the game developers referred to actions as "states", as evidenced by the "STA" label on one of the debug menus. The name "action" was chosen by the community as a less ambiguous alternative.

If Mario's current action is hacked to be an invalid action value, the game will either freeze or softlock, since such an action lacks associated code. There are 230 valid actions in the game, but some of these are accessible only through hacking. In addition to these, there are two "pseudo-actions", 0x050 and 0x051, that immediately transition to another action. Specifically, they are "begin sliding" actions, and they transition into either butt slide or stomach slide, depending on whether Mario is facing uphill or downhill. There is evidence of one action, action 0x00E, that was defined but whose code was never implemented.

Action groups

An action is represented as a 32-bit value. The lowest nine bits are a unique ID for the action, ranging in value from 0x000 to 0x192. Not all action IDs in this range are used by an action.

These IDs are divided into seven ranges, called action groups. These roughly categorize the behavior of each action, but are primarily used for organizational purposes in the code.

Name	Range start	Range end	Number of actions	Description
stationary	0x001	0x03F	36	stopped while on ground
moving	0x040	0x07F	40	moving while on ground
airborne	0x080	0x0BF	45	moving in air
submerged	0x0C0	0x0FF	32	in water, including with metal cap
cutscene	0x100	0x13F	51	no control of mario
automatic	0x140	0x17F	17	restricted control of mario
object	0x180	0x1BF	10	relating to picking up or releasing objects

The "uninitialized" action with ID 0x000 is not considered to be a part of any group. Despite being a valid action, it overrides much of Mario's behavior and is implemented differently than regular actions.

Action groups, while largely used for organization, do sometimes define shared properties of the actions contained in them. For example, the code for dying in quicksand is shared among the stationary, moving, and object action groups, so it is impossible to die from quicksand while in one of the other action groups.

Action flags

Most properties of actions are defined by action flags, which make up the remaining bits of the 32-bit action value. While there are 23 bits left after excluding the 9-bit ID, bit 30 is both unused by the game and unset by any action, so there are effectively only 22 action flags.

Bit	Name	Example properties
9	stationary	increases deceleration in water
10	moving	affects buoyancy in water, push speed of horizontal wind
11	airborne	allows stomping on enemies, affects knockback behavior, disallows lava boost
12	intangible	disallows object interaction
13	swimming	affects knockback behavior
14	metal water	affects knockback behavior, lessens gravity and terminal velocity
15	short hitbox	shortens Mario's object hitbox from 160 to 100
16	riding shell	makes water surface a tangible floor, allows attacking objects
17	invulnerable	disables certain interactions involving damage or knockback
18	butt/stomach slide	Klepto checks this flag; details not yet known
19	diving	determines which picking-up action is used, affects water entry
20	on pole	cannot grab pole when previous action has this flag set
21	hanging	affects knockback behavior
22	idle	animation plays when collecting cap, allows reading signs
23	attacking	slightly affects whether an object can pick Mario up
24	interruptable by wind	allows entering the vertical wind action
25	control jump height	strengthens gravity when not holding A on ascent
26	allow first person	allows C-up to affect action behavior
27	pause exit	the level exit option is shown in the pause menu
28	swimming/flying	unused by the game
29	water/text	unused by the game
31	throwing	something to do with particle effects; details not yet known

Note that the first three flags have the same name as the first three action groups. While most actions in these groups have the corresponding flag set, the converse is typically not true. Actions in the cutscene group, for example, may have the airborne flag set if they take place while Mario is in the air. There also exist unintuitive cases, such as action 0x036, air throw landing, which has the airborne flag set despite being a grounded stationary action, leading to strange behavior in some circumstances.

Frame

Whenever within a frame, execute_mario_action is called, and Mario's action is not "uninitialized", the following happens:

1. Reset Mario's model. The model animation will be updated within the action.
2. Why is so update_mario_inputs so complicated? Not even going into that.
3. If Mario's floor type is the death plane or... vertical wind, check warps, play SOUND_MARIO_WAAAOOOW.
4. If Mario's floor type is a warp, check warps.
5. If Mario's floor type is the PSS start or end tiles, start or end the timer.
6. If Mario's action does not have the (11) air or (13) swimming flags, the floor is SURFACE_BURNING (lava?), and Mario is not riding a shell and mario's is less than 10 units above the floor.
   1. Damage if not wearing metal cap, and set action to Lava Boost.
7. mario_process_interactions This can change mario's action.
8. Loop: Call the function that executes Mario's current action. Each action has associated code as stated above. Whenever the function is called, it can return TRUE, continuing the loop. Actions often call set_mario_action, which returns TRUE and processes yet another action. Theoretically, this could cause an infinite loop, however such a subframe transition sequence has not been found.
9. Adjust Mario's model for quicksand and squishing, adjust the camera, when submerged adjust the camera and spawn bubbles, update health, update cap hitbox and model, process wind and infinite stairs music.