diff --git a/gbsdk b/gbsdk
index 6b70e98..ac612c4 160000
--- a/gbsdk
+++ b/gbsdk
@@ -1 +1 @@
-Subproject commit 6b70e98c49b7be257020b732095cc4883669a9b8
+Subproject commit ac612c4c1a416d7b5cc42859e3dcc37f0d23dc77
diff --git a/src/actor.h b/src/actor.h
index ea3c96e..7773ce7 100644
--- a/src/actor.h
+++ b/src/actor.h
@@ -3,6 +3,8 @@
 
 #include <stdint.h>
 
+#include "mob.h"
+
 typedef enum {
     ANIM_STAND,
     ANIM_WALK,
@@ -44,7 +46,7 @@ void actor_reset(void);
  * @param id The ID of the mob to create
  * @return A pointer to the new actor or NULL if one could not be created
  */
-actor_t *actor_create_mob(uint8_t id);
+actor_t *actor_create_mob(mob_id_t id);
 
 /**
  * @brief Remove an actor from the screen.
diff --git a/src/mob.h b/src/mob.h
new file mode 100644
index 0000000..66ad96f
--- /dev/null
+++ b/src/mob.h
@@ -0,0 +1,9 @@
+#ifndef IS_MOB_H_
+#define IS_MOB_H_
+
+typedef enum {
+    MOB_ID_RAT,
+    MOB_ID_LIZARD,
+} mob_id_t;
+
+#endif