Add ball auto suggestion

click ball sprite/label to cycle through legal balls
hold alt to use old behavior (set to pokeball)
hold shift to cycle through legal balls randomly (default behavior goes
poke->color->poke)

want to randomize setting balls? use the ApplyBallLegalRandom method at
the end :)

can't really get too fancy as only one color is stored in the personal
data, pkm aren't one single color.

PKHeX.Core/Editing/BallRandomizer.cs

@@ -0,0 +1,152 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using static PKHeX.Core.Ball;
+
+namespace PKHeX.Core
+{
+    /// <summary>
+    /// Contains logic to apply a new <see cref="Ball"/> value to a <see cref="PKM"/>.
+    /// </summary>
+    public static class BallRandomizer
+    {
+        /// <summary>
+        /// Gets all balls that are legal for the input <see cref="PKM"/>.
+        /// </summary>
+        /// <param name="pkm">Pokémon to retrieve a list of valid balls for.</param>
+        /// <returns>Enumerable list of <see cref="Ball"/> values that the <see cref="PKM"/> is legal with.</returns>
+        public static IEnumerable<Ball> GetLegalBalls(PKM pkm)
+        {
+            var clone = pkm.Clone();
+            foreach (var b in BallList)
+            {
+                clone.Ball = (int)b;
+                if (new LegalityAnalysis(clone).Valid)
+                    yield return b;
+            }
+        }
+
+        /// <summary>
+        /// Applies a random legal ball value if any exist.
+        /// </summary>
+        /// <param name="pkm">Pokémon to modify.</param>
+        public static int ApplyBallLegalRandom(PKM pkm)
+        {
+            var balls = GetBallListFromColor(pkm).ToArray();
+            Util.Shuffle(balls);
+            return ApplyFirstLegalBall(pkm, balls);
+        }
+
+        /// <summary>
+        /// Applies a legal ball value if any exist, ordered by color.
+        /// </summary>
+        /// <param name="pkm">Pokémon to modify.</param>
+        public static int ApplyBallLegalByColor(PKM pkm)
+        {
+            var balls = GetBallListFromColor(pkm);
+            return ApplyFirstLegalBall(pkm, balls);
+        }
+
+        /// <summary>
+        /// Applies a random ball value in a cyclical manner.
+        /// </summary>
+        /// <param name="pkm">Pokémon to modify.</param>
+        public static int ApplyBallNext(PKM pkm)
+        {
+            var balls = GetBallList(pkm.Ball);
+            var next = balls.First();
+            return pkm.Ball = (int)next;
+        }
+
+        private static int ApplyFirstLegalBall(PKM pkm, IEnumerable<Ball> balls)
+        {
+            foreach (var b in balls)
+            {
+                pkm.Ball = (int)b;
+                if (new LegalityAnalysis(pkm).Valid)
+                    break;
+            }
+            return pkm.Ball;
+        }
+
+        private static IEnumerable<Ball> GetBallList(int ball)
+        {
+            var balls = BallList;
+            var currentBall = (Ball)ball;
+            return GetCircularOnce(balls, currentBall);
+        }
+
+        private static IEnumerable<Ball> GetBallListFromColor(PKM pkm)
+        {
+            var pi = PKX.Personal.GetFormeEntry(pkm.Species, pkm.AltForm);
+            var color = (PersonalColor)pi.Color;
+            var balls = BallColors[color];
+            var currentBall = (Ball)pkm.Ball;
+            return GetCircularOnce(balls, currentBall);
+        }
+
+        private static IEnumerable<T> GetCircularOnce<T>(T[] items, T current)
+        {
+            var currentIndex = Array.IndexOf(items, current);
+            if (currentIndex < 0)
+                currentIndex = items.Length - 2;
+            for (int i = currentIndex + 1; i < items.Length; i++)
+                yield return items[i];
+            for (int i = 0; i <= currentIndex; i++)
+                yield return items[i];
+        }
+
+        private static readonly Ball[] BallList = (Ball[]) Enum.GetValues(typeof(Ball));
+
+        static BallRandomizer()
+        {
+            var exclude = new[] {None, Poke};
+            var end = new[] {Poke};
+            var allBalls = BallList.Except(exclude).ToArray();
+            var colors = (PersonalColor[])Enum.GetValues(typeof(PersonalColor));
+            foreach (var c in colors)
+            {
+                var vals = BallColors[c];
+                var extra = allBalls.Except(vals).ToArray();
+                Util.Shuffle(extra);
+                BallColors[c] = vals.Concat(extra).Concat(end).ToArray();
+            }
+        }
+
+        /// <summary>
+        /// Priority Match ball IDs that match the color ID in descending order
+        /// </summary>
+        private static readonly Dictionary<PersonalColor, Ball[]> BallColors = new Dictionary<PersonalColor, Ball[]>
+        {
+            [PersonalColor.Red] =    new[] { Cherish, Repeat, Fast, Heal, Great, Dream },
+            [PersonalColor.Blue] =   new[] { Dive, Net, Great, Beast },
+            [PersonalColor.Yellow] = new[] { Level, Ultra, Repeat, Quick, Moon },
+            [PersonalColor.Green] =  new[] { Safari, Friend, Nest, Dusk },
+            [PersonalColor.Black] =  new[] { Luxury, Heavy, Ultra, Moon, Net, Beast },
+
+            [PersonalColor.Brown] =  new[] { Level, Heavy },
+            [PersonalColor.Purple] = new[] { Master, Love, Dream, Heal },
+            [PersonalColor.Gray] =   new[] { Heavy, Premier, Luxury },
+            [PersonalColor.White] =  new[] { Premier, Timer, Luxury, Ultra },
+            [PersonalColor.Pink] =   new[] { Love, Dream, Heal },
+        };
+
+        /// <summary>
+        /// Personal Data color IDs
+        /// </summary>
+        private enum PersonalColor : byte
+        {
+            Red,
+            Blue,
+            Yellow,
+            Green,
+            Black,
+
+            Brown,
+            Purple,
+            Gray,
+            White,
+            Pink,
+        }
+    }
+}

PKHeX.WinForms/Controls/PKM Editor/PKMEditor.cs

@@ -576,7 +576,17 @@ namespace PKHeX.WinForms.Controls
             }
         }
 
-        private void ClickBall(object sender, EventArgs e) => CB_Ball.SelectedIndex = 0;
+        private void ClickBall(object sender, EventArgs e)
+        {
+            pkm.Ball = WinFormsUtil.GetIndex(CB_Ball);
+            if (ModifierKeys.HasFlag(Keys.Alt))
+                CB_Ball.SelectedValue = (int)Ball.Poke;
+            else if (ModifierKeys.HasFlag(Keys.Shift))
+                CB_Ball.SelectedValue = BallRandomizer.ApplyBallLegalRandom(pkm);
+            else
+                CB_Ball.SelectedValue = BallRandomizer.ApplyBallLegalByColor(pkm);
+        }
+
         private void ClickShinyLeaf(object sender, EventArgs e) => ShinyLeaf.CheckAll(ModifierKeys != Keys.Control);
 
         private void ClickMetLocation(object sender, EventArgs e)