Gen 3 introduced Dive, a field move that can reach the seafloor, as HM08. Fully implementing Dive is fairly complicated: its in-battle effect is similar to Dig and Fly but not exactly the same, and its field effect requires a lot of changes.

(The code for this feature was adapted from [Pokémon Orange](https://github.com/PiaCarrot/pokeorange/).)

[Here](https://github.com/Rangi42/pokecrystal/commit/c21561ea717feef9b2eb3785c2ea112cd0d19ba0) are all the changes needed to implement Dive, applied to a copy of pokecrystal. You can `clone` [Rangi42/pokecrystal](https://github.com/Rangi42/pokecrystal/tree/dive) and `checkout` the `dive` branch to test it for yourself.

![Screenshot](screenshots/dive.png)


## TOC

TODO


## 1. Start to prepare the Dive move

First, we have to add the move Dive, following [this tutorial](Add-a-new-move).

Replace `MOVE_OR_ANIM_FC` with `DIVE`; give it a name, description, and battle properties (`DIVE, EFFECT_FLY, 80, WATER, 100, 10, 0`); and add it to Pokémon learnsets (Seel and Dewgong learn it by level-up).

We still have to implement the move animation, so let's do that next.


## 2. Create the Dive move animation

Refer to a new tutorial for adding new move animations, including new graphics and objects.

- constants/battle_anim_constants.asm
- data/battle_anims/objects.asm
- data/moves/animations.asm


## 3. Using Dive hides the Pokémon underwater

Edit [constants/battle_constants.asm](../blob/master/constants/battle_constants.asm):

```diff
 ; wPlayerSubStatus4 or wEnemySubStatus4 bit flags
 	enum_start 7, -1
 	enum SUBSTATUS_LEECH_SEED
 	enum SUBSTATUS_RAGE
 	enum SUBSTATUS_RECHARGE
 	enum SUBSTATUS_SUBSTITUTE
-	enum SUBSTATUS_UNKNOWN_1
+	enum SUBSTATUS_UNDERWATER
 	enum SUBSTATUS_FOCUS_ENERGY
 	enum SUBSTATUS_MIST
 	enum SUBSTATUS_X_ACCURACY
```

Edit [engine/battle/core.asm](../blob/master/engine/battle/core.asm):

```diff
 ResidualDamage:
 ; Return z if the user fainted before
 ; or as a result of residual damage.
 ; For Sandstorm damage, see HandleWeather.

 	...

 	call SwitchTurnCore
 	xor a
 	ld [wNumHits], a
 	ld de, ANIM_SAP
 	ld a, BATTLE_VARS_SUBSTATUS3_OPP
 	call GetBattleVar
 	and 1 << SUBSTATUS_FLYING | 1 << SUBSTATUS_UNDERGROUND
+	jr nz, .not_flying_or_underground
+	call Call_PlayBattleAnim_OnlyIfVisible
+	jr .called
+.not_flying_or_underground
+	ld a, BATTLE_VARS_SUBSTATUS4_OPP
+	call GetBattleVar
+	and 1 << SUBSTATUS_UNDERWATER
 	call z, Call_PlayBattleAnim_OnlyIfVisible
+.called
 	call SwitchTurnCore
```

```diff
 HandleWrap:
 	...

 	ld a, BATTLE_VARS_SUBSTATUS3
 	call GetBattleVar
 	and 1 << SUBSTATUS_FLYING | 1 << SUBSTATUS_UNDERGROUND
 	jr nz, .skip_anim
+
+	ld a, BATTLE_VARS_SUBSTATUS4
+	call GetBattleVar
+	and 1 << SUBSTATUS_UNDERWATER
+	jr nz, .skip_anim

 	call SwitchTurnCore
 	xor a
 	ld [wNumHits], a
 	ld [wFXAnimID + 1], a
 	predef PlayBattleAnim
 	call SwitchTurnCore

 .skip_anim
 	...
```

```diff
 Call_PlayBattleAnim_OnlyIfVisible:
 	ld a, BATTLE_VARS_SUBSTATUS3
 	call GetBattleVar
 	and 1 << SUBSTATUS_FLYING | 1 << SUBSTATUS_UNDERGROUND
 	ret nz
+
+	ld a, BATTLE_VARS_SUBSTATUS4
+	call GetBattleVar
+	and 1 << SUBSTATUS_UNDERWATER
+	ret nz

 Call_PlayBattleAnim:
 	ld a, e
 	ld [wFXAnimID], a
 	ld a, d
 	ld [wFXAnimID + 1], a
 	call WaitBGMap
 	predef_jump PlayBattleAnim
```

Edit [engine/battle/effect_commands.asm](../blob/master/engine/battle/effect_commands.asm):

TODO

Edit [engine/battle_anims/bg_effects.asm](../blob/master/engine/battle_anims/bg_effects.asm):

```diff
 BGEffect_CheckFlyDigStatus:
 	ld hl, BG_EFFECT_STRUCT_BATTLE_TURN
 	add hl, bc
 	ldh a, [hBattleTurn]
 	and $1
 	xor [hl]
 	jr nz, .player
 	ld a, [wEnemySubStatus3] ; EnemySubStatus3
 	and 1 << SUBSTATUS_FLYING | 1 << SUBSTATUS_UNDERGROUND
+	ret nz
+	ld a, [wEnemySubStatus4]
+	and 1 << SUBSTATUS_UNDERWATER
 	ret

 .player
 	ld a, [wPlayerSubStatus3] ; PlayerSubStatus3
 	and 1 << SUBSTATUS_FLYING | 1 << SUBSTATUS_UNDERGROUND
+	ret nz
+	ld a, [wPlayerSubStatus4]
+	and 1 << SUBSTATUS_UNDERWATER
 	ret
```

Edit [engine/battle/ai/scoring.asm](../blob/master/engine/battle/ai/scoring.asm):

```diff
 AI_Smart_Fly:
-; Fly, Dig
+; Fly, Dig, Dive

 ; Greatly encourage this move if the player is
-; flying or underground, and slower than the enemy.
+; flying, underground, or underwater, and slower than the enemy.

 	ld a, [wPlayerSubStatus3]
 	and 1 << SUBSTATUS_FLYING | 1 << SUBSTATUS_UNDERGROUND
+	jr nz, .player_hidden
+	ld a, [wPlayerSubStatus4]
+	and 1 << SUBSTATUS_UNDERWATER
 	ret z

+.player_hidden
 	call AICompareSpeed
 	ret nc

 	dec [hl]
 	dec [hl]
 	dec [hl]
 	ret
```

```diff
 AI_Smart_PriorityHit:
 	call AICompareSpeed
 	ret c

-; Dismiss this move if the player is flying or underground.
+; Dismiss this move if the player is flying, underground, or underwater.
 	ld a, [wPlayerSubStatus3]
 	and 1 << SUBSTATUS_FLYING | 1 << SUBSTATUS_UNDERGROUND
 	jp nz, AIDiscourageMove
+	ld a, [wPlayerSubStatus4]
+	and 1 << SUBSTATUS_UNDERWATER
+	jp nz, AIDiscourageMove

 ; Greatly encourage this move if it will KO the player.
 	...
```

```diff
 AI_Smart_FutureSight:
 ; Greatly encourage this move if the player is
-; flying or underground, and slower than the enemy.
+; flying, underground, or underwater, and slower than the enemy.

 	call AICompareSpeed
 	ret nc

 	ld a, [wPlayerSubStatus3]
 	and 1 << SUBSTATUS_FLYING | 1 << SUBSTATUS_UNDERGROUND
+	jr nz, .player_hidden
+	ld a, [wPlayerSubStatus4]
+	and 1 << SUBSTATUS_UNDERWATER
 	ret z

+.player_hidden
 	dec [hl]
 	dec [hl]
 	ret
```


## 4. Surf and Whirlpool do double damage to underwater Pokémon

Refer to [this tutorial](Add-a-new-move-effect).

- constants/move_effect_constants.asm
- data/moves/moves.asm (again)
- data/moves/effects_pointers.asm
- data/moves/effects.asm
- macros/scripts/battle_commands.asm
- data/battle/effect_command_pointers.asm
- engine/battle/effect_commands.asm (again)
- engine/battle/ai/scoring.asm (again)


## 5. Prepare the HM08 item

We also have to add the item HM08, following [this tutorial](Add-a-new-TM-or-HM).

Add an HM for `DIVE`; give it a name and attributes (`0, HELD_NONE, 0, CANT_SELECT | CANT_TOSS, TM_HM, ITEMMENU_PARTY, ITEMMENU_NOUSE`); associate it with the move `DIVE`; make it unforgettable; and add it to Pokémon base learnsets (50 Pokémon are compatible with it).


## 6. Define collision types for Dive water

- constants/collision_constants.asm
- data/collision_permissions.asm
- engine/overworld/tile_events.asm


## 7. Start to prepare the Dive field move effect

Now we can start to add the field move effect, following [this tutorial](Add-a-new-field-move-effect).

Define `MONMENUITEM_DIVE`; associate it with the move `DIVE`; and implement `MonMenu_Dive` for its menu action (in [engine/pokemon/mon_menu.asm](../blob/master/engine/pokemon/mon_menu.asm), or [engine/menus/start_menu.asm](../blob/master/engine/menus/start_menu.asm) in older versions of pokecrystal) like this:

```diff
+MonMenu_Dive:
+	farcall DiveFunction
+	ld a, [wFieldMoveSucceeded]
+	cp $1
+	jr nz, .Fail
+	ld b, $4
+	ld a, $2
+	ret
+
+.Fail:
+	ld a, $3
+	ret
```

We still have to implement `DiveFunction`; but first, let's define some more components for it.


## 8. Define a utility function to check for Dive water

- home/map_objects.asm


## 9. Define text related to using Dive

- data/text/common_2.asm


## 10. Define the `divemap` and `divewarp` event commands

- wram.asm
- macros/scripts/events.asm
- engine/overworld/scripting.asm
- home/flag.asm
- engine/overworld/warp_connection.asm


## 11. Finish the Dive field move effect

- engine/events/overworld.asm


## 12. Press A on Dive water to use Dive

- engine/overworld/events.asm


## 13. Design a sprite for swimming underwater

Let's add a unique sprite for the player being underwater, following [this tutorial](Add-a-new-overworld-sprite).

Define `SPRITE_DIVE` as a regular sprite constant; give it properties (`DiveSpriteGFX, 12, WALKING_SPRITE, PAL_OW_BLUE`); and create `DiveSpriteGFX` as **gfx/sprites/dive.png**:

![gfx/sprites/dive.png](screenshots/gfx-sprites-dive.png)

Note that this is the Surfing sprite from Gen 1, which resembles a Seel. It's appropriate for Dive since Seel learns Dive by level-up.


## 14. Use the sprite for the player when underwater

- constants/wram_constants.asm
- data/sprites/player_sprites.asm
- engine/events/overworld.asm (again)
- engine/overworld/map_setup.asm
- engine/overworld/player_movement.asm


## 15. Start creating a unique tileset for underwater maps

Refer to [this tutorial](Add-a-new-tileset).

- constants/tileset_constants.asm
- gfx/tilesets/underwater.png
- gfx/tilesets/underwater_palette_map.asm
- data/tilesets/underwater_metatiles.bin
- data/tilesets/underwater_collision.asm
- data/tilesets.asm
- gfx/tileset_palette_maps.asm
- gfx/tilesets.asm


## 16. Can't Fly while underwater

- engine/events/overworld.asm (again)


## 17. Fix bugs that affect the Dive features

- engine/overworld/overworld.asm
- home/map.asm


## 18. Animate underwater seaweed and bubbles

Refer to a new tutorial for adding new animated tiles.

- gfx/tilesets/bubble/1.png
- gfx/tilesets/bubble/2.png
- gfx/tilesets/bubble/3.png
- gfx/tilesets/bubble/4.png
- gfx/tilesets/bubble/5.png
- gfx/tilesets/seaweed/1.png
- gfx/tilesets/seaweed/2.png
- engine/tilesets/tileset_anims.asm


## 19. Use special palettes for underwater tiles and sprites

Refer to a new tutorial for adding new special palettes, including map (tile) and object (sprite) palettes.

- gfx/tilesets/underwater.pal
- gfx/tilesets/underwater_sprites.pal
- engine/tilesets/tileset_palettes.asm
- engine/gfx/color.asm


## 20. Add deep water to an overworld tileset

Refer to a new tutorial for adding new animated tiles.

- gfx/tilesets/johto.png
- gfx/tilesets/johto_palette_map.asm
- data/tilesets/johto_collision.asm
- data/tilesets/johto_metatiles.bin
- gfx/tilesets/water/deep-water.png
- engine/tilesets/tileset_anims.asm (again)


## 21. Add a map with Dive spots

Refer to [this tutorial](Add-a-new-map-object-movement-behavior).

- maps/Route41.blk
- maps/Route41.asm
- maps/Route41Underwater.blk
- maps/Route41Underwater.asm
- constants/event_flags.asm (again)
- constants/map_constants.asm
- data/maps/maps.asm
- data/maps/attributes.asm
- data/wild/johto_grass.asm
- data/maps/blocks.asm
- data/maps/scripts.asm
- data/maps/roofs.asm
- data/maps/outdoor_sprites.asm