We've got enemies and movement!!

Assets/_Project/Scripts/Gameplay/WaveDefinition.cs

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+// Assets/_Project/Scripts/Gameplay/WaveDefinition.cs
+using System;
+using UnityEngine;
+
+namespace TD.Gameplay
+{
+    /// <summary>
+    /// A single spawn group within a wave: one enemy type, how many of them,
+    /// and how long to wait between each spawn.
+    /// </summary>
+    [Serializable]
+    public struct WaveEntry
+    {
+        [Tooltip("The enemy type to spawn for this group.")]
+        public EnemyDefinition EnemyType;
+
+        [Tooltip("How many enemies of this type to spawn.")]
+        public int Count;
+
+        [Tooltip("Seconds between each individual spawn within this group. " +
+                 "0 = all spawn simultaneously.")]
+        public float SpawnInterval;
+    }
+
+    /// <summary>
+    /// Defines the composition of a single wave. One asset per wave; referenced in
+    /// order by <see cref="WaveManager.waveDefinitions"/>.
+    /// </summary>
+    /// <remarks>
+    /// Entries are processed in array order. Multiple entries let designers mix enemy
+    /// types within one wave (e.g. 10 fast scouts followed by 3 armoured brutes).
+    /// The wave is not considered complete until all spawned enemies are dead or have
+    /// leaked — not just until all entries are spawned.
+    /// </remarks>
+    [CreateAssetMenu(fileName = "WaveDefinition", menuName = "TD/Wave Definition", order = 4)]
+    public class WaveDefinition : ScriptableObject
+    {
+        [Tooltip("Seconds between the wave-number advancing (start of prep) and the " +
+                 "first enemy spawning. Gives players time to build before the wave hits.")]
+        public float PrepTime = 10f;
+
+        [Tooltip("Enemy groups that make up this wave. Processed in order.")]
+        public WaveEntry[] Entries;
+    }
+}