diff --git a/src/board.rs b/src/board.rs
index 884b39e..07a56d6 100644
--- a/src/board.rs
+++ b/src/board.rs
@@ -1,4 +1,4 @@
-use std::sync::Arc;
+use std::sync::{Arc, Mutex};
 
 use anyhow::Result;
 use engine::prelude::{
@@ -8,13 +8,13 @@ use engine::prelude::{
 
 use crate::{game::MillGame, objects::Objects};
 
-#[derive(Debug, PartialEq, Clone, Copy)]
+#[derive(Debug)]
 pub struct BoardSlot {
     pub x: usize,
     pub y: usize,
     pub z: usize,
 
-    pub state: BoardSlotState,
+    pub state: Mutex<BoardSlotState>,
     pub position: Vector2<f32>,
     pub slot_marker: Option<Entity>,
 }
@@ -45,7 +45,7 @@ impl BoardSlot {
             y,
             z,
 
-            state: BoardSlotState::default(),
+            state: Mutex::new(BoardSlotState::default()),
             position,
             slot_marker: Some(scene.add_entity(marker)?),
         })
@@ -57,7 +57,7 @@ impl BoardSlot {
             y,
             z,
 
-            state: BoardSlotState::Invalid,
+            state: Mutex::new(BoardSlotState::Invalid),
             position: vec2(0.0, 0.0),
             slot_marker: None,
         }
@@ -101,18 +101,18 @@ impl BoardSlot {
     }
 
     pub fn valid(&self) -> bool {
-        self.state != BoardSlotState::Invalid
+        *self.state.lock().unwrap() != BoardSlotState::Invalid
     }
 
     pub fn white(&self) -> bool {
-        match self.state {
+        match *self.state.lock().unwrap() {
             BoardSlotState::White(_) => true,
             _ => false,
         }
     }
 
     pub fn black(&self) -> bool {
-        match self.state {
+        match *self.state.lock().unwrap() {
             BoardSlotState::Black(_) => true,
             _ => false,
         }
@@ -279,7 +279,7 @@ impl Board {
         for outer in self.slots.iter_mut() {
             for inner in outer.iter_mut() {
                 for slot in inner.iter_mut() {
-                    if slot.state != BoardSlotState::Invalid {
+                    if *slot.state.lock().unwrap() != BoardSlotState::Invalid {
                         if (slot.position - position).magnitude() <= DISTANCE {
                             return Some(slot);
                         }
diff --git a/src/game.rs b/src/game.rs
index a001139..a846979 100644
--- a/src/game.rs
+++ b/src/game.rs
@@ -404,12 +404,12 @@ impl MillGame {
             PlayerColor::White => {
                 Self::log(&format!("place white stone"));
 
-                slot.state = BoardSlotState::White(stone.stone);
+                *slot.state.lock().unwrap() = BoardSlotState::White(stone.stone);
             }
             PlayerColor::Black => {
                 Self::log(&format!("place black stone"));
 
-                slot.state = BoardSlotState::Black(stone.stone);
+                *slot.state.lock().unwrap() = BoardSlotState::Black(stone.stone);
             }
         }
 
@@ -426,7 +426,7 @@ impl MillGame {
     pub fn remove_stone(slot: &mut BoardSlot, scene: &mut Scene) -> Result<()> {
         Self::log("remove_stone");
 
-        let entity = match slot.state {
+        let entity = match *slot.state.lock().unwrap() {
             BoardSlotState::Black(e) => {
                 Self::log(&format!("\tremove black stone"));
 
@@ -441,8 +441,9 @@ impl MillGame {
         };
 
         scene.remove_entity(entity)?;
+        Self::log("\t -> TODO: set stone state to Dead");
 
-        slot.state = BoardSlotState::Empty;
+        *slot.state.lock().unwrap() = BoardSlotState::Empty;
 
         Ok(())
     }
@@ -613,7 +614,10 @@ impl EngineObject for MillGame {
                                     *self.current_player.lock().unwrap()
                                 ));
 
-                                if match (slot.state, *self.current_player.lock().unwrap()) {
+                                if match (
+                                    *slot.state.lock().unwrap(),
+                                    *self.current_player.lock().unwrap(),
+                                ) {
                                     (BoardSlotState::Black(_), PlayerColor::White) => true,
                                     (BoardSlotState::White(_), PlayerColor::Black) => true,
                                     _ => false,
diff --git a/src/simple_ai.rs b/src/simple_ai.rs
index b2e9935..5abd32d 100644
--- a/src/simple_ai.rs
+++ b/src/simple_ai.rs
@@ -34,7 +34,7 @@ impl SimpleAI {
                         .iter_mut()
                         .flatten()
                         .flatten()
-                        .filter(|slot| slot.state == BoardSlotState::Empty)
+                        .filter(|slot| *slot.state.lock().unwrap() == BoardSlotState::Empty)
                         .collect();
 
                     let len = free_slots.len();
@@ -53,11 +53,13 @@ impl SimpleAI {
                     .iter_mut()
                     .flatten()
                     .flatten()
-                    .filter(|slot| match (slot.state, self.player_color) {
-                        (BoardSlotState::Black(_), PlayerColor::White) => true,
-                        (BoardSlotState::White(_), PlayerColor::Black) => true,
-                        _ => false,
-                    })
+                    .filter(
+                        |slot| match (*slot.state.lock().unwrap(), self.player_color) {
+                            (BoardSlotState::Black(_), PlayerColor::White) => true,
+                            (BoardSlotState::White(_), PlayerColor::Black) => true,
+                            _ => false,
+                        },
+                    )
                     .collect();
 
                 let len = other_color.len();
@@ -70,7 +72,92 @@ impl SimpleAI {
                     Ok(())
                 })?;
             }
-            GameState::Main => todo!(),
+            GameState::Main => {
+                let mut same_color: Vec<&BoardSlot> = board
+                    .iter()
+                    .flatten()
+                    .flatten()
+                    .filter(
+                        |slot| match (*slot.state.lock().unwrap(), self.player_color) {
+                            (BoardSlotState::White(_), PlayerColor::White) => true,
+                            (BoardSlotState::Black(_), PlayerColor::Black) => true,
+                            _ => false,
+                        },
+                    )
+                    .collect();
+
+                loop {
+                    let len = same_color.len();
+                    let slot = &mut same_color[Random::range(0, len as u32) as usize];
+
+                    // find free neighbour field
+                    if let Some(neighbour) = match Random::range(0, 6) as usize {
+                        0 => {
+                            if slot.x > 0 {
+                                Some(&board[slot.x - 1][slot.y][slot.z])
+                            } else {
+                                None
+                            }
+                        }
+                        1 => {
+                            if slot.x < 2 {
+                                Some(&board[slot.x + 1][slot.y][slot.z])
+                            } else {
+                                None
+                            }
+                        }
+                        2 => {
+                            if slot.y > 0 {
+                                Some(&board[slot.x][slot.y - 1][slot.z])
+                            } else {
+                                None
+                            }
+                        }
+                        3 => {
+                            if slot.y < 2 {
+                                Some(&board[slot.x][slot.y + 1][slot.z])
+                            } else {
+                                None
+                            }
+                        }
+                        4 => {
+                            if slot.z > 0 {
+                                Some(&board[slot.x][slot.y][slot.z - 1])
+                            } else {
+                                None
+                            }
+                        }
+                        5 => {
+                            if slot.z < 2 {
+                                Some(&board[slot.x][slot.y][slot.z + 1])
+                            } else {
+                                None
+                            }
+                        }
+                        // 6 => ,
+                        // 7 => ,
+                        // 8 => ,
+                        // 9 => ,
+                        _ => unreachable!(),
+                    } {
+                        let mut neighbour_state = neighbour.state.lock().unwrap();
+                        let mut slot_state = slot.state.lock().unwrap();
+
+                        match (*neighbour_state, *slot_state) {
+                            (BoardSlotState::Empty, BoardSlotState::Black(e)) => {
+                                *neighbour_state = BoardSlotState::Black(e);
+                                *slot_state = BoardSlotState::Empty;
+                            }
+                            (BoardSlotState::Empty, BoardSlotState::White(e)) => {
+                                *neighbour_state = BoardSlotState::White(e);
+                                *slot_state = BoardSlotState::Empty;
+                            }
+
+                            _ => (),
+                        }
+                    }
+                }
+            }
         }
 
         MillGame::log("finish AI");