Implemented Startling Development

Mage.Sets/src/mage/cards/s/StartlingDevelopment.java

@@ -0,0 +1,45 @@
+package mage.cards.s;
+
+import mage.abilities.costs.mana.ManaCostsImpl;
+import mage.abilities.effects.common.continuous.BecomesCreatureTargetEffect;
+import mage.abilities.keyword.CyclingAbility;
+import mage.cards.CardImpl;
+import mage.cards.CardSetInfo;
+import mage.constants.CardType;
+import mage.constants.Duration;
+import mage.constants.SubType;
+import mage.game.permanent.token.custom.CreatureToken;
+import mage.target.common.TargetCreaturePermanent;
+
+import java.util.UUID;
+
+/**
+ * @author TheElk801
+ */
+public final class StartlingDevelopment extends CardImpl {
+
+    public StartlingDevelopment(UUID ownerId, CardSetInfo setInfo) {
+        super(ownerId, setInfo, new CardType[]{CardType.INSTANT}, "{1}{U}");
+
+        // Until end of turn, target creature becomes a blue Serpent with base power and toughness 4/4.
+        this.getSpellAbility().addEffect(new BecomesCreatureTargetEffect(
+                new CreatureToken(
+                        4, 4, "blue Serpent with base power and toughness 4/4"
+                ).withColor("U").withSubType(SubType.SERPENT),
+                false, false, Duration.EndOfTurn
+        ).setRemoveSubtypes(true));
+        this.getSpellAbility().addTarget(new TargetCreaturePermanent());
+
+        // Cycling {1}
+        this.addAbility(new CyclingAbility(new ManaCostsImpl("{1}")));
+    }
+
+    private StartlingDevelopment(final StartlingDevelopment card) {
+        super(card);
+    }
+
+    @Override
+    public StartlingDevelopment copy() {
+        return new StartlingDevelopment(this);
+    }
+}

Mage.Sets/src/mage/sets/IkoriaLairOfBehemoths.java

@@ -275,6 +275,7 @@ public final class IkoriaLairOfBehemoths extends ExpansionSet {
         cards.add(new SetCardInfo("Spontaneous Flight", 33, Rarity.COMMON, mage.cards.s.SpontaneousFlight.class));
         cards.add(new SetCardInfo("Springjaw Trap", 241, Rarity.COMMON, mage.cards.s.SpringjawTrap.class));
         cards.add(new SetCardInfo("Sprite Dragon", 211, Rarity.UNCOMMON, mage.cards.s.SpriteDragon.class));
+        cards.add(new SetCardInfo("Startling Development", 68, Rarity.COMMON, mage.cards.s.StartlingDevelopment.class));
         cards.add(new SetCardInfo("Sudden Spinnerets", 171, Rarity.COMMON, mage.cards.s.SuddenSpinnerets.class));
         cards.add(new SetCardInfo("Suffocating Fumes", 100, Rarity.COMMON, mage.cards.s.SuffocatingFumes.class));
         cards.add(new SetCardInfo("Survivors' Bond", 172, Rarity.COMMON, mage.cards.s.SurvivorsBond.class));

Mage/src/main/java/mage/abilities/effects/common/continuous/BecomesCreatureTargetEffect.java

@@ -22,6 +22,7 @@ public class BecomesCreatureTargetEffect extends ContinuousEffectImpl {
     protected boolean addStillALandText;
     protected boolean loseName;
     protected boolean keepAbilities;
+    protected boolean removeSubtypes = false;
 
 
     public BecomesCreatureTargetEffect(Token token, boolean loseAllAbilities, boolean stillALand, Duration duration) {
@@ -86,6 +87,9 @@ public class BecomesCreatureTargetEffect extends ContinuousEffectImpl {
                                 permanent.getCardType().clear(); // remove all CardTypes
                                 permanent.getSubtype(game).addAll(token.getSubtype(game));
                             } else {
+                                if (removeSubtypes) {
+                                    permanent.getSubtype(game).clear();
+                                }
                                 for (SubType t : token.getSubtype(game)) {
                                     if (!permanent.hasSubtype(t, game)) {
                                         permanent.getSubtype(game).add(t);
@@ -149,6 +153,11 @@ public class BecomesCreatureTargetEffect extends ContinuousEffectImpl {
         return result;
     }
 
+    public BecomesCreatureTargetEffect setRemoveSubtypes(boolean removeSubtypes) {
+        this.removeSubtypes = removeSubtypes;
+        return this;
+    }
+
     @Override
     public boolean apply(Game game, Ability source) {
         return false;