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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.

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[1].