AI: reworked blockers selections:

* now computer will use simplified 1 vs 1 combat damage simulations to choose better blockers (due better game score after combat);
* it's not a full combat simulation, but support many things like non-stack abilities, damage replacement effects and SBA -- much better than older PT compare (related to #13290);
* now AI correctly use a blockers with deathtouth, indestructible, first/double strike and other abilities;
* chump blocks also supported (chump logic implemented before in 92b7ed8efc, related to #4485);

Mage.Server.Plugins/Mage.Player.AI.MA/src/mage/player/ai/util/CombatUtil.java

@@ -1,10 +1,13 @@
 package mage.player.ai.util;
 
+import mage.abilities.Ability;
+import mage.abilities.common.SimpleStaticAbility;
 import mage.abilities.keyword.DoubleStrikeAbility;
 import mage.abilities.keyword.InfectAbility;
 import mage.counters.CounterType;
 import mage.game.Game;
 import mage.game.combat.Combat;
+import mage.game.combat.CombatGroup;
 import mage.game.events.GameEvent;
 import mage.game.permanent.Permanent;
 import mage.game.turn.CombatDamageStep;
@@ -203,7 +206,7 @@ public final class CombatUtil {
                 blockedCount++;
             }
 
-            // find good sacrifices
+            // find good sacrifices (chump blocks also supported due bad game score on loose)
             // TODO: add chump blocking support here?
             // TODO: there are many triggers on damage, attack, etc - it can't be processed without real game simulations
             if (blocker == null) {
@@ -339,13 +342,38 @@ public final class CombatUtil {
         // so blocker will block same creature with same score without penalty
         int startScore = GameStateEvaluator2.evaluate(defendingPlayerId, sim, false).getTotalScore();
 
-        // fake game simulation (manual PT calculation)
+        // fake combat simulation (simple damage simulation)
+        Permanent simAttacker = sim.getPermanent(attacker.getId());
+        Permanent simBlocker = sim.getPermanent(blocker.getId());
+        if (simAttacker == null || simBlocker == null) {
+            throw new IllegalArgumentException("Broken sim game, can't find attacker or blocker");
+        }
+        // don't ask about that hacks - just replace to real combat simulation someday (another hack but with full stack resolve)
+        // first damage step
+        simulateCombatDamage(sim, simBlocker, simAttacker, true);
+        simulateCombatDamage(sim, simAttacker, simBlocker, true);
+        simAttacker.applyDamage(sim);
+        simBlocker.applyDamage(sim);
+        sim.checkStateAndTriggered();
+        sim.processAction();
+        // second damage step
+        if (sim.getPermanent(simBlocker.getId()) != null && sim.getPermanent(simAttacker.getId()) != null) {
+            simulateCombatDamage(sim, simBlocker, simAttacker, false);
+            simulateCombatDamage(sim, simAttacker, simBlocker, false);
+            simAttacker.applyDamage(sim);
+            simBlocker.applyDamage(sim);
+            sim.checkStateAndTriggered();
+            sim.processAction();
+        }
+
+        /* old manual PT compare
         if (attacker.getPower().getValue() >= blocker.getToughness().getValue()) {
             sim.getBattlefield().removePermanent(blocker.getId());
         }
         if (attacker.getToughness().getValue() <= blocker.getPower().getValue()) {
             sim.getBattlefield().removePermanent(attacker.getId());
         }
+         */
 
         // fake non-block simulation
         simNonBlocking.getPlayer(defendingPlayerId).damage(
@@ -356,6 +384,7 @@ public final class CombatUtil {
                 true,
                 true
         );
+        simNonBlocking.checkStateAndTriggered();
         simNonBlocking.processAction();
 
         int endBlockingScore = GameStateEvaluator2.evaluate(defendingPlayerId, sim, false).getTotalScore();
@@ -368,6 +397,15 @@ public final class CombatUtil {
         );
     }
 
+    private static void simulateCombatDamage(Game sim, Permanent fromCreature, Permanent toCreature, boolean isFirstDamageStep) {
+        Ability fakeAbility = new SimpleStaticAbility(null);
+        if (CombatGroup.dealsDamageThisStep(fromCreature, isFirstDamageStep, sim)) {
+            fakeAbility.setSourceId(fromCreature.getId());
+            fakeAbility.setControllerId(fromCreature.getControllerId());
+            toCreature.damage(fromCreature.getPower().getValue(), fromCreature.getId(), fakeAbility, sim, true, true);
+        }
+    }
+
     private static void simulateStep(Game sim, Step step) {
         sim.getPhase().setStep(step);
         if (!step.skipStep(sim, sim.getActivePlayerId())) {

Mage.Tests/src/test/java/org/mage/test/AI/basic/BlockSimulationAITest.java

@@ -6,6 +6,22 @@ import org.junit.Test;
 import org.mage.test.serverside.base.CardTestPlayerBaseWithAIHelps;
 
 /**
+ * Combat's blocking tests
+ * <p>
+ * TODO: add tests with multi blocker requirement effects
+ * <p>
+ * Supported abilities:
+ * - DeathtouchAbility - supported, has tests
+ * - FirstStrikeAbility - supported, has tests
+ * - DoubleStrikeAbility - ?
+ * - IndestructibleAbility - supported, need tests
+ * - FlyingAbility - ?
+ * - ReachAbility - ?
+ * - ExaltedAbility - ?
+ * - Trample + Deathtouch
+ * - combat damage and die triggers - need to implement full combat simulation with stack resolve, see CombatUtil->willItSurviveSimple
+ * - other use cases, see https://github.com/magefree/mage/issues/4485
+ *
  * @author JayDi85
  */
 public class BlockSimulationAITest extends CardTestPlayerBaseWithAIHelps {
@@ -242,12 +258,55 @@ public class BlockSimulationAITest extends CardTestPlayerBaseWithAIHelps {
         assertDamageReceived(playerB, "Spectral Bears", 2);
     }
 
-    // TODO: add tests with multi blocker requirement effects
+    @Test
-    // TODO: add tests for DeathtouchAbility
+    public void test_Block_1_attacker_vs_first_strike() {
-    // TODO: add tests for FirstStrikeAbility
+        addCard(Zone.BATTLEFIELD, playerA, "Balduvian Bears", 1); // 2/2
-    // TODO: add tests for DoubleStrikeAbility
+        //
-    // TODO: add tests for IndestructibleAbility
+        addCard(Zone.BATTLEFIELD, playerB, "Arbor Elf", 1); // 1/1
-    // TODO: add tests for FlyingAbility
+        addCard(Zone.BATTLEFIELD, playerB, "White Knight", 1); // 2/2 with first strike
-    // TODO: add tests for ReachAbility
+        addCard(Zone.BATTLEFIELD, playerB, "Spectral Bears", 1); // 3/3
-    // TODO: add tests for ExaltedAbility???
+        addCard(Zone.BATTLEFIELD, playerB, "Deadbridge Goliath", 1); // 5/5
+        addCard(Zone.BATTLEFIELD, playerB, "Colossal Dreadmaw", 1); // 6/6
+
+        attack(1, playerA, "Balduvian Bears");
+
+        // ai must use smaller blocker and survive (2/2 with first strike must block 2/2)
+        aiPlayStep(1, PhaseStep.DECLARE_BLOCKERS, playerB);
+        checkBlockers("x1 optimal blocker", 1, playerB, "White Knight");
+
+        setStopAt(1, PhaseStep.END_TURN);
+        setStrictChooseMode(true);
+        execute();
+
+        assertLife(playerA, 20);
+        assertLife(playerB, 20);
+        assertGraveyardCount(playerA, "Balduvian Bears", 1);
+        assertDamageReceived(playerB, "White Knight", 0); // due first strike
+    }
+
+    @Test
+    public void test_Block_1_attacker_vs_deathtouch() {
+        addCard(Zone.BATTLEFIELD, playerA, "Balduvian Bears", 1); // 2/2
+        //
+        addCard(Zone.BATTLEFIELD, playerB, "Arbor Elf", 1); // 1/1
+        addCard(Zone.BATTLEFIELD, playerB, "Arashin Cleric", 1); // 1/3
+        addCard(Zone.BATTLEFIELD, playerB, "Graveblade Marauder", 1); // 1/4 with deathtouch
+        addCard(Zone.BATTLEFIELD, playerB, "Deadbridge Goliath", 1); // 5/5
+        addCard(Zone.BATTLEFIELD, playerB, "Colossal Dreadmaw", 1); // 6/6
+
+        attack(1, playerA, "Balduvian Bears");
+
+        // ai must use smaller blocker to kill and survive (1/4 with deathtouch must block 2/2 -- not a smaller 1/3)
+        aiPlayStep(1, PhaseStep.DECLARE_BLOCKERS, playerB);
+        checkBlockers("x1 optimal blocker", 1, playerB, "Graveblade Marauder");
+
+        setStopAt(1, PhaseStep.END_TURN);
+        setStrictChooseMode(true);
+        execute();
+
+        assertLife(playerA, 20);
+        assertLife(playerB, 20);
+        assertGraveyardCount(playerA, "Balduvian Bears", 1);
+        assertDamageReceived(playerB, "Graveblade Marauder", 2);
+    }
 }

Mage/src/main/java/mage/game/combat/CombatGroup.java

@@ -243,7 +243,7 @@ public class CombatGroup implements Serializable, Copyable<CombatGroup> {
      * @param first true for first strike damage step, false for normal damage step
      * @return true if permanent should deal damage this step
      */
-    private boolean dealsDamageThisStep(Permanent perm, boolean first, Game game) {
+    public static boolean dealsDamageThisStep(Permanent perm, boolean first, Game game) {
         if (perm == null) {
             return false;
         }