fix #12928 (The Mindskinner)

Mage.Sets/src/mage/cards/t/TheMindskinner.java

@@ -66,11 +66,12 @@ public TheMindskinnerEffect copy() {
 
     @Override
     public boolean replaceEvent(GameEvent event, Ability source, Game game) {
+        int amount = event.getAmount();
         preventDamageAction(event, source, game);
         for (UUID playerId : game.getOpponents(source.getControllerId())) {
             Player player = game.getPlayer(playerId);
             if (player != null) {
-                player.millCards(event.getAmount(), source, game);
+                player.millCards(amount, source, game);
             }
         }
         return true;

Mage.Tests/src/test/java/org/mage/test/cards/replacement/prevent/TheMindskinnerTest.java

@@ -0,0 +1,39 @@
+package org.mage.test.cards.replacement.prevent;
+
+import mage.constants.PhaseStep;
+import mage.constants.Zone;
+import org.junit.Test;
+import org.mage.test.serverside.base.CardTestPlayerBase;
+
+public class TheMindskinnerTest extends CardTestPlayerBase {
+
+    private static final String mindskinner = "The Mindskinner"; // 10/1 can't be blocked
+    // If a source you control would deal damage to an opponent, prevent that damage and each opponent mills that many cards.
+
+    private static final String piker = "Goblin Piker"; // 2/1
+
+    private static final String bolt = "Lightning Bolt";
+
+    @Test
+    public void testPreventionAndMill() {
+        addCard(Zone.BATTLEFIELD, playerA, mindskinner);
+        addCard(Zone.BATTLEFIELD, playerA, piker);
+        addCard(Zone.HAND, playerA, bolt);
+        addCard(Zone.BATTLEFIELD, playerA, "Mountain");
+
+        castSpell(1, PhaseStep.PRECOMBAT_MAIN, playerA, bolt, playerB);
+
+        attack(1, playerA, piker, playerB);
+
+        setStrictChooseMode(true);
+        setStopAt(1, PhaseStep.POSTCOMBAT_MAIN);
+        execute();
+
+        assertLife(playerA, 20);
+        assertLife(playerB, 20);
+
+        assertGraveyardCount(playerA, 1); // bolt
+        assertGraveyardCount(playerB, 5);
+    }
+
+}