diff --git a/Mage.Server.Plugins/Mage.Player.AIMCTS/src/mage/player/ai/ComputerPlayerMCTS.java b/Mage.Server.Plugins/Mage.Player.AIMCTS/src/mage/player/ai/ComputerPlayerMCTS.java
index e5b3b2eeea4..aa20af794a3 100644
--- a/Mage.Server.Plugins/Mage.Player.AIMCTS/src/mage/player/ai/ComputerPlayerMCTS.java
+++ b/Mage.Server.Plugins/Mage.Player.AIMCTS/src/mage/player/ai/ComputerPlayerMCTS.java
@@ -94,8 +94,10 @@ public class ComputerPlayerMCTS extends ComputerPlayer {
             root = new MCTSNode(playerId, sim);
         }
         applyMCTS(game, action);
-        root = root.bestChild();
-        root.emancipate();
+        if (root != null && root.bestChild() != null) {
+            root = root.bestChild();
+            root.emancipate();
+        }
     }
 
     protected void getNextAction(Game game, NextAction nextAction) {
diff --git a/Mage.Tests/src/test/java/org/mage/test/cards/requirement/BecomeBlockTriggersMonteCarloAITest.java b/Mage.Tests/src/test/java/org/mage/test/cards/requirement/BecomeBlockTriggersMonteCarloAITest.java
index f060372581e..503d3f2b52b 100644
--- a/Mage.Tests/src/test/java/org/mage/test/cards/requirement/BecomeBlockTriggersMonteCarloAITest.java
+++ b/Mage.Tests/src/test/java/org/mage/test/cards/requirement/BecomeBlockTriggersMonteCarloAITest.java
@@ -2,15 +2,86 @@ package org.mage.test.cards.requirement;
 
 import mage.constants.PhaseStep;
 import mage.constants.Zone;
+import org.junit.Ignore;
 import org.junit.Test;
 import org.mage.test.serverside.base.CardTestPlayerBaseWithMonteCarloAIHelps;
 
 /**
  * @author JayDi85
  */
+@Ignore // TODO: research and fix attack/block simulations
 public class BecomeBlockTriggersMonteCarloAITest extends CardTestPlayerBaseWithMonteCarloAIHelps {
 
-    // continue from BecomeBlockTriggersTest
+    @Test
+    public void test_AI_Block_NoBlockers() {
+        addCard(Zone.BATTLEFIELD, playerA, "Grizzly Bears", 1); // 2/2
+
+        attack(1, playerA, "Grizzly Bears");
+
+        aiPlayStep(1, PhaseStep.DECLARE_BLOCKERS, playerB);
+
+        setStopAt(1, PhaseStep.END_TURN);
+        setStrictChooseMode(true);
+        execute();
+
+        assertLife(playerB, 20 - 2);
+        assertPermanentCount(playerA, 1);
+    }
+
+    @Test
+    public void test_AI_Block_KillAttackerAndAlive() {
+        addCard(Zone.BATTLEFIELD, playerA, "Grizzly Bears", 1); // 2/2
+        //
+        addCard(Zone.BATTLEFIELD, playerB, "Apex Devastator", 1); // 10/10
+
+        attack(1, playerA, "Grizzly Bears");
+        aiPlayStep(1, PhaseStep.DECLARE_BLOCKERS, playerB);
+
+        setStopAt(1, PhaseStep.END_TURN);
+        setStrictChooseMode(true);
+        execute();
+
+        assertLife(playerB, 20);
+        assertPermanentCount(playerA, 0);
+        assertPermanentCount(playerB, 1);
+    }
+
+    @Test
+    public void test_AI_Block_KillAttackerAndDie() {
+        addCard(Zone.BATTLEFIELD, playerA, "Atarka Efreet", 1); // 5/1
+        //
+        addCard(Zone.BATTLEFIELD, playerB, "Aarakocra Sneak", 1); // 1/4
+
+        attack(1, playerA, "Atarka Efreet");
+        aiPlayStep(1, PhaseStep.DECLARE_BLOCKERS, playerB);
+
+        setStopAt(1, PhaseStep.END_TURN);
+        setStrictChooseMode(true);
+        execute();
+
+        assertLife(playerB, 20);
+        assertPermanentCount(playerA, 1);
+        assertPermanentCount(playerB, 1);
+    }
+
+    @Test
+    public void test_AI_Block_BlockAttackerAndDie() {
+        addCard(Zone.BATTLEFIELD, playerA, "Apex Devastator", 1);// 10/10
+        //
+        addCard(Zone.BATTLEFIELD, playerB, "Grizzly Bears", 1); // 2/2
+
+        attack(1, playerA, "Apex Devastator");
+        aiPlayStep(1, PhaseStep.DECLARE_BLOCKERS, playerB);
+
+        setStopAt(1, PhaseStep.END_TURN);
+        setStrictChooseMode(true);
+        execute();
+
+        assertLife(playerB, 20);
+        assertPermanentCount(playerA, 1);
+        assertPermanentCount(playerB, 0);
+    }
+
     @Test
     public void test_AI_CantBlockAgain() {
         // Monte Carlo bug: Triggered ability triggered twice (should be once), see https://github.com/magefree/mage/issues/6367