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.
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.
Actions can transition to other actions within a frame. Whenever an action changes to another through returning a call to set_mario_action, it returns `TRUE` which continues a loop. Theoretically, this could cause an infinite loop, however such a transition sequence has not been found.[1]
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.[2]