diff --git a/include/LICENSE.txt b/include/LICENSE.txt
new file mode 100644
index 00000000..fba5620c
--- /dev/null
+++ b/include/LICENSE.txt
@@ -0,0 +1,23 @@
+NOTE: The following license applies only to the files within this directory.
+
+MIT License
+
+Copyright (c) 2022 UsernameFodder
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
\ No newline at end of file
diff --git a/include/dungeon_mode.h b/include/dungeon_mode.h
new file mode 100644
index 00000000..8d60214c
--- /dev/null
+++ b/include/dungeon_mode.h
@@ -0,0 +1,71 @@
+#ifndef PMDSKY_DUNGEON_MODE_H
+#define PMDSKY_DUNGEON_MODE_H
+
+#include "graphics.h"
+
+// Used in various contexts, like with entity positions in the dungeon
+struct position {
+    s16 x;
+    s16 y;
+};
+
+// Used to indicate the pixel position of an entity. Values are shifted 8 bits to the left, so they
+// are probably decimal numbers instead.
+struct pixel_position {
+    u32 x;
+    u32 y;
+};
+
+// Entity type. This is used to tag generic entity pointers.
+enum entity_type {
+    ENTITY_NOTHING = 0,
+    ENTITY_MONSTER = 1,
+    ENTITY_TRAP = 2,
+    ENTITY_ITEM = 3,
+    ENTITY_HIDDEN_STAIRS = 5,
+    // Used when a temporary instance of this struct is created to pass it to some
+    // function that requires it as a parameter
+    ENTITY_TEMPORARY = 6,
+};
+
+// Generic entity data
+struct entity {
+    enum entity_type type;                  // 0x0
+    struct position pos;                    // 0x4
+    struct position prev_pos;               // 0x8
+    struct pixel_position pixel_pos;        // 0xC
+    struct pixel_position pixel_pos_mirror; // 0x14: Monsters only?
+    // 0x1C: Graphical parameter for evelation above the ground. Last byte behaves weirdly.
+    s32 elevation;
+    u8 is_visible; // 0x20: For traps/hidden stairs
+    u8 field_0x21;
+    // 0x22: If true, the sprite will be shown with a certain degree of transparency
+    u8 transparent;
+    // 0x23: Seems to be the animation frame counter for the 10-frame "shuffle" animation that
+    // plays at the end of a walk sequence
+    u8 end_walk_anim_frame;
+    u8 field_0x24;
+    u8 room_idx; // 0x25: Index of the room a monster is in. 0xFF for hall
+    // 0x26: Unique index for each monster that spawns. Starts at 0xA for the leader, and each
+    // subsequent monster to spawn is assigned the next number (0xB, 0xC, ...)
+    u16 spawn_genid;
+    u8 field_0x28;
+    u8 field_0x29;
+    u8 field_0x2a;
+    u8 field_0x2b;
+    struct animation_control anim_ctrl;
+    u16 sprite_index; // 0xA8
+    u8 field_0xaa;
+    u8 field_0xab;
+    u8 field_0xac;
+    u8 field_0xad;
+    u8 animation_group_id;        // 0xAE
+    u8 animation_group_id_mirror; // 0xAF
+    u8 animation_id;              // 0xB0
+    u8 animation_id_mirror0;      // 0xB1
+    u8 field_0xb2;
+    u8 field_0xb3;
+    void* info; // 0xB4: Points to info struct for monster/item/trap
+};
+
+#endif //PMDSKY_DUNGEON_MODE_H
\ No newline at end of file
diff --git a/include/graphics.h b/include/graphics.h
new file mode 100644
index 00000000..4ec03154
--- /dev/null
+++ b/include/graphics.h
@@ -0,0 +1,89 @@
+#ifndef PMDSKY_GRAPHICS_H
+#define PMDSKY_GRAPHICS_H
+
+#include "util.h"
+#include "wan.h"
+
+struct wan_offset {
+    struct uvec2_16 head;
+    struct uvec2_16 hand_left;
+    struct uvec2_16 hand_right;
+    struct uvec2_16 center;
+};
+
+struct wan_palettes {
+    struct rgba* palette_bytes;
+    u16 unk1;
+    u16 nb_color;
+    u16 unk2;
+    u16 unk3;
+    s32 unk4; // Normally always 0
+};
+
+// Contains data relating to animation.
+// Mentioned under the name of "AnimeCtrl" in a debug message.
+struct animation_control {
+    u16 some_bitfield;
+    u16 field1_0x2;
+    u16 field2_0x4;
+    u16 anim_frame_duration;
+    u16 field4_0x8;
+    u16 field5_0xa;
+    u16 field6_0xc; // (from struct entity) animation frame counter for the idle animation?
+    u8 field7_0xe;
+    u8 field8_0xf;
+    // appears to be a structure used for unknown purpose with 6 2-byte value
+    u16 field9_0x10[6];
+    u16 field10_0x1c;
+    u16 field11_0x1e;
+    struct vec2_16 anim_frame_offset;
+    struct vec2_16 anim_frame_shadow_offset;
+    s32 anim_frame_flag;
+    s32 anim_frame_flag_sum;     // ORed from the current WAN animation frame flag
+    u16 animations_or_group_len; // number of animation group Chara sprites, other number of
+                                      // animation in the first animation group
+    u16 field19_0x32;
+    u8 field20_0x34;
+    u8 field21_0x35;
+    u16 field22_0x36; // seems to be an index into the wan fragments table
+    u16 field23_0x38;
+    u16 anim_frame_frame_id;
+    u16 field25_0x3c;
+    u8 field26_0x3e;
+    u8 field27_0x3f;
+    // Used to determine where to store the palette's colors. Multiplied by 0x100
+    u8 palette_pos_high;
+    u8 palette_pos_low; // Used to determine where to store the palette's colors
+    u8 field30_0x42;
+    u8 field31_0x43;
+    u8 field32_0x44;
+    u8 field33_0x45;
+    u8 field34_0x46;
+    u8 field35_0x47;
+    struct wan_animation_frame* first_animation_frame; // first frame in animation group
+    struct wan_animation_frame* next_animation_frame;
+    struct wan_offset* wan_offsets;
+    u8* wan_frames;
+    void** wan_fragments_byte_store;
+    struct wan_palettes* wan_palettes;
+    u16 wan_is_256_color;
+    u16 loop_start; // same meaning as in struct wan_animation_frame
+    u8 field44_0x64;
+    u8 field45_0x65;
+    u8 field46_0x66;
+    u8 field47_0x67;
+    // seems to point to a SIRO file containing another sprite, that is sometimes used instead of
+    // the one specified in loaded_sprite_id (maybe it is loaded_sprite_id but looked up?)
+    u8* sprite_override;
+    u32 field49_0x6c;
+    u16 loaded_sprite_id; // id in the WAN_TABLE static list
+    u16 field51_0x72;
+    u8 field52_0x74;
+    u8 field53_0x75;
+    u16 animation_group_id;
+    u16 animation_id;
+    u8 palette_bank;
+    u8 field57_0x7b;
+};
+
+#endif //PMDSKY_GRAPHICS_H
\ No newline at end of file
diff --git a/include/overlay_29_022E0354.h b/include/overlay_29_022E0354.h
index 3d98d03e..4ee09003 100644
--- a/include/overlay_29_022E0354.h
+++ b/include/overlay_29_022E0354.h
@@ -1,6 +1,8 @@
 #ifndef PMDSKY_OVERLAY_29_022E0354_H
 #define PMDSKY_OVERLAY_29_022E0354_H
 
-u8 EntityIsValid__022E0354(s32 *entity);
+#include "dungeon_mode.h"
+
+u8 EntityIsValid__022E0354(struct entity *entity);
 
 #endif //PMDSKY_OVERLAY_29_022E0354_H
diff --git a/include/util.h b/include/util.h
new file mode 100644
index 00000000..602a0ab6
--- /dev/null
+++ b/include/util.h
@@ -0,0 +1,24 @@
+#ifndef PMDSKY_UTIL_H
+#define PMDSKY_UTIL_H
+
+// RGBA8 structure. Sometimes alpha is ignored and only used for padding
+struct rgba {
+    u8 r;
+    u8 b;
+    u8 g;
+    u8 a; // Sometimes used only for padding
+};
+
+// a 2d short (16bit) vector
+struct vec2_16 {
+    s16 x;
+    s16 y;
+};
+
+// a 2d ushort (16bit) vector
+struct uvec2_16 {
+    u16 x;
+    u16 y;
+};
+
+#endif //PMDSKY_UTIL_H
\ No newline at end of file
diff --git a/include/wan.h b/include/wan.h
new file mode 100644
index 00000000..8f686ddc
--- /dev/null
+++ b/include/wan.h
@@ -0,0 +1,14 @@
+#ifndef PMDSKY_WAN_H
+#define PMDSKY_WAN_H
+
+#include "util.h"
+
+struct wan_animation_frame {
+    u8 duration;
+    u8 flag;
+    u16 frame_id;
+    struct vec2_16 offset;
+    struct vec2_16 shadow_offset;
+};
+
+#endif //PMDSKY_WAN_H
\ No newline at end of file
diff --git a/src/overlay_29_022E0354.c b/src/overlay_29_022E0354.c
index 124f7df9..220d6690 100644
--- a/src/overlay_29_022E0354.c
+++ b/src/overlay_29_022E0354.c
@@ -1,10 +1,10 @@
 #include "overlay_29_022E0354.h"
 
-u8 EntityIsValid__022E0354(s32 *entity)
+u8 EntityIsValid__022E0354(struct entity *entity)
 {
     if (entity == NULL)
     {
         return FALSE;
     }
-    return *entity != 0;
+    return entity->type != ENTITY_NOTHING;
 }