diff --git a/Mage.Sets/src/mage/cards/m/MageDuel.java b/Mage.Sets/src/mage/cards/m/MageDuel.java
index d51a36f166..502c08c1b2 100644
--- a/Mage.Sets/src/mage/cards/m/MageDuel.java
+++ b/Mage.Sets/src/mage/cards/m/MageDuel.java
@@ -75,8 +75,7 @@ enum MageDuelCondition implements Condition {
                 .stream()
                 .filter(Objects::nonNull)
                 .filter(spell -> spell.isInstantOrSorcery(game))
-                .map(Spell::getSourceId)
-                .anyMatch(source.getSourceId()::equals);
+                .anyMatch(spell -> !spell.getSourceId().equals(source.getSourceId()));
     }
 
     @Override
diff --git a/Mage.Tests/src/test/java/org/mage/test/cards/single/stx/MageDuelTest.java b/Mage.Tests/src/test/java/org/mage/test/cards/single/stx/MageDuelTest.java
new file mode 100644
index 0000000000..1f47ec58e8
--- /dev/null
+++ b/Mage.Tests/src/test/java/org/mage/test/cards/single/stx/MageDuelTest.java
@@ -0,0 +1,174 @@
+package org.mage.test.cards.single.stx;
+
+import mage.constants.ManaType;
+import mage.constants.PhaseStep;
+import mage.constants.Zone;
+import org.junit.Test;
+import org.mage.test.serverside.base.CardTestPlayerBase;
+
+/**
+ * {@link mage.cards.m.MageDuel Mage Duel}
+ * {2}{G}
+ * Instant
+ * <p>
+ * This spell costs {2} less to cast if you’ve cast another instant or sorcery spell this turn.
+ * <p>
+ * Target creature you control gets +1/+2 until end of turn.
+ * Then it fights target creature you don’t control.
+ * (Each deals damage equal to its power to the other.)
+ *
+ * @author Alex-Vasile
+ */
+public class MageDuelTest extends CardTestPlayerBase {
+
+    private static final String mageDuel = "Mage Duel";
+    // Instant
+    // {W}
+    // You gain hexproof until your next turn. You gain 2 life.
+    private static final String blossomingCalm = "Blossoming Calm";
+    // Sorcery
+    // {W}
+    // You gain 2 life for each creature you control.
+    private static final String festivalOfTrokin = "Festival of Trokin";
+
+    // Creature you control
+    // 1/1
+    private static final String akroanJailer = "Akroan Jailer";
+    // Creature you don't control
+    // 2/2
+    private static final String lion = "Silvercoat Lion";
+
+    /**
+     * Test that the spell costs {2}{G} if no other spell was cast
+     */
+    @Test
+    public void testCostReductionNotAlwaysOn() {
+        addCard(Zone.HAND, playerA, mageDuel);
+        addCard(Zone.HAND, playerA, "Forest");
+        addCard(Zone.BATTLEFIELD, playerA, "Forest", 2);
+        addCard(Zone.BATTLEFIELD, playerA, akroanJailer);
+
+        addCard(Zone.BATTLEFIELD, playerB, lion);
+
+        checkPlayableAbility("Can't cast for {1}{G}", 1, PhaseStep.PRECOMBAT_MAIN, playerA, "Cast" + mageDuel, false);
+        playLand(1, PhaseStep.PRECOMBAT_MAIN, playerA, "Forest");
+        castSpell(1, PhaseStep.PRECOMBAT_MAIN, playerA, mageDuel);
+
+        setStopAt(1, PhaseStep.POSTCOMBAT_MAIN);
+        execute();
+        assertPowerToughness(playerA, akroanJailer, 2, 3);
+        assertPermanentCount(playerA, akroanJailer, 1);
+        assertGraveyardCount(playerB, lion, 1);
+    }
+
+    /**
+     * Test cost reduction does not apply to itself.
+     * If you have {2}{G} to pay for it, it should still cost {2}{G} rather than {G}
+     */
+    @Test
+    public void testDoesntDiscountItself() {
+        addCard(Zone.HAND, playerA, mageDuel);
+        addCard(Zone.BATTLEFIELD, playerA, "Forest", 3);
+        addCard(Zone.BATTLEFIELD, playerA, akroanJailer);
+
+        addCard(Zone.BATTLEFIELD, playerB, lion);
+
+        castSpell(1, PhaseStep.PRECOMBAT_MAIN, playerA, mageDuel);
+
+        setStopAt(1, PhaseStep.POSTCOMBAT_MAIN);
+        execute();
+        assertPowerToughness(playerA, akroanJailer, 2, 3);
+        assertPermanentCount(playerA, akroanJailer, 1);
+        assertGraveyardCount(playerB, lion, 1);
+        assertManaPool(playerA, ManaType.GREEN, 0);
+        assertTappedCount("Forest", true, 3);
+    }
+
+    /**
+     * Test that the cost reduction works with instant spells.
+     */
+    @Test
+    public void testInstantCostReduction() {
+        addCard(Zone.HAND, playerA, mageDuel);
+        addCard(Zone.HAND, playerA, blossomingCalm);
+        addCard(Zone.BATTLEFIELD, playerA, "Plains");
+        addCard(Zone.BATTLEFIELD, playerA, "Forest");
+        addCard(Zone.BATTLEFIELD, playerA, akroanJailer);
+
+        addCard(Zone.BATTLEFIELD, playerB, lion);
+
+        castSpell(1, PhaseStep.PRECOMBAT_MAIN, playerA, blossomingCalm);
+        waitStackResolved(1, PhaseStep.PRECOMBAT_MAIN);
+        castSpell(1, PhaseStep.PRECOMBAT_MAIN, playerA, mageDuel);
+
+        setStopAt(1, PhaseStep.POSTCOMBAT_MAIN);
+        execute();
+        assertPowerToughness(playerA, akroanJailer, 2, 3);
+        assertPermanentCount(playerA, akroanJailer, 1);
+        assertGraveyardCount(playerB, lion, 1);
+        assertLife(playerA, 20 + 2);
+    }
+
+    /**
+     * Test that the cost reduction works with sorcery spells.
+     */
+    @Test
+    public void testSorceryCostReduction() {
+        addCard(Zone.HAND, playerA, mageDuel);
+        addCard(Zone.HAND, playerA, festivalOfTrokin);
+        addCard(Zone.BATTLEFIELD, playerA, "Plains");
+        addCard(Zone.BATTLEFIELD, playerA, "Forest");
+        addCard(Zone.BATTLEFIELD, playerA, akroanJailer);
+
+        addCard(Zone.BATTLEFIELD, playerB, lion);
+
+        castSpell(1, PhaseStep.PRECOMBAT_MAIN, playerA, festivalOfTrokin);
+        waitStackResolved(1, PhaseStep.PRECOMBAT_MAIN);
+        castSpell(1, PhaseStep.PRECOMBAT_MAIN, playerA, mageDuel);
+
+        setStopAt(1, PhaseStep.POSTCOMBAT_MAIN);
+        execute();
+        assertPowerToughness(playerA, akroanJailer, 2, 3);
+        assertPermanentCount(playerA, akroanJailer, 1);
+        assertGraveyardCount(playerB, lion, 1);
+        assertLife(playerA, 20 + 2);
+    }
+
+    /**
+     * Test that it works if a instant/sorcery card is copied and then cast
+     */
+    @Test
+    public void testCopiedCardCast() {
+        String isochronScpeter = "Isochron Scepter";
+        addCard(Zone.HAND, playerA, isochronScpeter);
+        addCard(Zone.HAND, playerA, mageDuel);
+        addCard(Zone.HAND, playerA, blossomingCalm);
+        addCard(Zone.BATTLEFIELD, playerA, "Forest", 1 + 2 + 2);
+        addCard(Zone.BATTLEFIELD, playerA, akroanJailer);
+
+        addCard(Zone.BATTLEFIELD, playerB, lion);
+
+        setStrictChooseMode(true);
+
+        castSpell(1, PhaseStep.PRECOMBAT_MAIN, playerA, isochronScpeter);
+        setChoice(playerA, "Yes");
+        setChoice(playerA, blossomingCalm);
+        waitStackResolved(1, PhaseStep.PRECOMBAT_MAIN);
+
+        activateAbility(1, PhaseStep.PRECOMBAT_MAIN, playerA, "{2}, {T}:");
+        setChoice(playerA, "Yes");
+        setChoice(playerA, "Yes");
+
+        waitStackResolved(1, PhaseStep.PRECOMBAT_MAIN);
+        castSpell(1, PhaseStep.PRECOMBAT_MAIN, playerA, mageDuel);
+        addTarget(playerA, akroanJailer);
+        addTarget(playerA, lion);
+
+        setStopAt(1, PhaseStep.POSTCOMBAT_MAIN);
+        execute();
+        assertPowerToughness(playerA, akroanJailer, 2, 3);
+        assertPermanentCount(playerA, akroanJailer, 1);
+        assertGraveyardCount(playerB, lion, 1);
+        assertLife(playerA, 20 + 2);
+    }
+}