Dominaria packs will now be guaranteed to have at least one legendary creature

Mage/src/main/java/mage/cards/ExpansionSet.java

@@ -83,7 +83,7 @@ public abstract class ExpansionSet implements Serializable {
             return this.cardNumber;
         }
 
-        public int getCardNumberAsInt(){
+        public int getCardNumberAsInt() {
             return CardUtil.parseCardNumberAsInt(this.cardNumber);
         }
 
@@ -121,6 +121,7 @@ public abstract class ExpansionSet implements Serializable {
     protected int numBoosterRare;
     protected int numBoosterDoubleFaced; // -1 = include normally 0 = exclude  1-n = include explicit
     protected int ratioBoosterMythic;
+    protected boolean needsLegends = false;
 
     protected int maxCardNumberInBooster; // used to omit cards with collector numbers beyond the regular cards in a set for boosters
 
@@ -210,6 +211,20 @@ public abstract class ExpansionSet implements Serializable {
     }
 
     public List<Card> createBooster() {
+        if (needsLegends) {
+            for (int i = 0; i < 100000; i++) {//don't want to somehow loop forever
+                List<Card> booster = tryBooster();
+                for (Card card : booster) {
+                    if (card.isLegendary() && card.isCreature()) {// Dominaria packs must contain at least one legendary creature.
+                        return booster;
+                    }
+                }
+            }
+        }
+        return tryBooster();
+    }
+
+    public List<Card> tryBooster() {
         List<Card> booster = new ArrayList<>();
         if (!hasBoosters) {
             return booster;
@@ -436,6 +451,8 @@ public abstract class ExpansionSet implements Serializable {
         savedCards.clear();
     }
 
-    public int getMaxCardNumberInBooster() { return maxCardNumberInBooster; }
+    public int getMaxCardNumberInBooster() {
+        return maxCardNumberInBooster;
+    }
 
 }