diff --git a/src/main.rs b/src/main.rs
index 897616f..48b13b0 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -315,6 +315,7 @@ impl GameState for State {
                 while new_runstate == RunState::Ticking {
                     self.run_systems();
                     self.ecs.maintain();
+                    try_spawn_interval(&mut self.ecs);
                     match *self.ecs.fetch::<RunState>() {
                         RunState::AwaitingInput => new_runstate = RunState::AwaitingInput,
                         RunState::MagicMapReveal { row, cursed } => {
diff --git a/src/map/interval_spawning_system.rs b/src/map/interval_spawning_system.rs
new file mode 100644
index 0000000..fd9afa3
--- /dev/null
+++ b/src/map/interval_spawning_system.rs
@@ -0,0 +1,60 @@
+use crate::{gamelog, raws, spawner, Clock, Map, RandomNumberGenerator, TakingTurn};
+use specs::prelude::*;
+
+const TRY_SPAWN_CHANCE: i32 = 70;
+
+pub fn try_spawn_interval(ecs: &mut World) {
+    let mut try_spawn = false;
+    // Scope for borrow checker (ECS)
+    {
+        let map = ecs.fetch::<Map>();
+        // Difficulty 0 maps shouldn't have respawning hostile mobs.
+        if map.difficulty == 0 {
+            return;
+        }
+        let clock = ecs.read_storage::<Clock>();
+        let turns = ecs.read_storage::<TakingTurn>();
+        let mut rng = ecs.write_resource::<rltk::RandomNumberGenerator>();
+        for (_c, _t) in (&clock, &turns).join() {
+            if rng.roll_dice(1, TRY_SPAWN_CHANCE) == 1 {
+                rltk::console::log("Trying spawn.");
+                try_spawn = true;
+            }
+        }
+    }
+    if try_spawn {
+        spawn_random_mob_in_free_nonvisible_tile(ecs);
+    }
+}
+
+fn spawn_random_mob_in_free_nonvisible_tile(ecs: &mut World) {
+    let map = ecs.fetch::<Map>();
+    let available_tiles = populate_unblocked_nonvisible_tiles(&map);
+    let difficulty = (map.difficulty + gamelog::get_event_count("player_level")) / 2;
+    if available_tiles.len() == 0 {
+        return;
+    }
+    let mut rng = ecs.write_resource::<RandomNumberGenerator>();
+    let idx = get_random_idx_from_possible_tiles(&mut rng, available_tiles);
+    let key = spawner::mob_table(difficulty).roll(&mut rng);
+    let x = idx as i32 % map.width;
+    let y = idx as i32 / map.width;
+    std::mem::drop(map);
+    std::mem::drop(rng);
+    raws::spawn_named_entity(&raws::RAWS.lock().unwrap(), ecs, &key, raws::SpawnType::AtPosition { x, y }, difficulty);
+}
+
+fn populate_unblocked_nonvisible_tiles(map: &Map) -> Vec<usize> {
+    let mut tiles: Vec<usize> = Vec::new();
+    for (i, _tile) in map.tiles.iter().enumerate() {
+        if !map.blocked[i] && !map.visible_tiles[i] {
+            tiles.push(i);
+        }
+    }
+    return tiles;
+}
+
+fn get_random_idx_from_possible_tiles(rng: &mut rltk::RandomNumberGenerator, area: Vec<usize>) -> usize {
+    let idx = if area.len() == 1 { 0usize } else { (rng.roll_dice(1, area.len() as i32) - 1) as usize };
+    return idx;
+}
diff --git a/src/map/mod.rs b/src/map/mod.rs
index 2c7e1df..31fcd3c 100644
--- a/src/map/mod.rs
+++ b/src/map/mod.rs
@@ -6,6 +6,8 @@ pub mod colours;
 mod glyphs;
 mod tiletype;
 pub use tiletype::{tile_cost, tile_opaque, tile_walkable, TileType};
+mod interval_spawning_system;
+pub use interval_spawning_system::try_spawn_interval;
 pub mod themes;
 
 // FIXME: If the map size gets too small, entities stop being rendered starting from the right.
diff --git a/src/raws/rawmaster.rs b/src/raws/rawmaster.rs
index 2e69c91..b9a456f 100644
--- a/src/raws/rawmaster.rs
+++ b/src/raws/rawmaster.rs
@@ -228,6 +228,8 @@ pub fn spawn_named_mob(
                     "BLOCKS_TILE" => eb = eb.with(BlocksTile {}),
                     "BYSTANDER" => eb = eb.with(Bystander {}),
                     "MONSTER" => eb = eb.with(Monster {}),
+                    "SMALL_GROUP" => {} // These flags are for region spawning,
+                    "LARGE_GROUP" => {} // and don't matter here (yet)?
                     "MULTIATTACK" => {
                         eb = eb.with(MultiAttack {});
                         xp_value += 3;
@@ -463,18 +465,17 @@ fn get_renderable_component(renderable: &super::item_structs::Renderable) -> cra
 }
 
 pub fn table_by_name(raws: &RawMaster, key: &str, difficulty: i32) -> RandomTable {
+    let upper_bound = difficulty;
+    let lower_bound = if key != "mobs" { 0 } else { difficulty / 6 };
     if raws.table_index.contains_key(key) {
         let spawn_table = &raws.raws.spawn_tables[raws.table_index[key]];
 
         use super::SpawnTableEntry;
 
-        let upper_bound = difficulty;
-        let lower_bound = if key != "mobs" { 0 } else { difficulty / 6 };
-
         let available_options: Vec<&SpawnTableEntry> = spawn_table
             .table
             .iter()
-            .filter(|entry| entry.difficulty > lower_bound && entry.difficulty <= upper_bound)
+            .filter(|entry| entry.difficulty >= lower_bound && entry.difficulty <= upper_bound)
             .collect();
 
         let mut rt = RandomTable::new();
@@ -487,8 +488,8 @@ pub fn table_by_name(raws: &RawMaster, key: &str, difficulty: i32) -> RandomTabl
         }
     }
     rltk::console::log(format!(
-        "DEBUGINFO: Something went wrong when trying to spawn {} @ map difficulty {}. Returned debug entry.",
-        key, difficulty
+        "DEBUGINFO: Something went wrong when trying to spawn {} @ map difficulty {} [upper bound: {}, lower bound: {}]. Returned debug entry.",
+        key, difficulty, upper_bound, lower_bound
     ));
     return RandomTable::new().add("debug", 1);
 }