Add project files.

AlientAttack.MonoGame/Things/Items/Item.cs

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+using Microsoft.Xna.Framework;
+using Microsoft.Xna.Framework.Graphics;
+using System;
+
+namespace AlienAttack.MonoGame.Things.Items;
+
+internal abstract class Item : MoveableSprite
+{
+    private Vector2 _anchor;        // the "center" the item orbits around
+    private float _t;               // radians
+    private float _radius = 6f;     // pixels (small circle)
+    private float _omega = 2.2f;    // radians/sec (speed of orbit)
+    private float _scale = 1f;
+
+    protected string? TextureName;
+
+    public Item(int x, int y) : base(x, y)
+    {
+        YVelocity = .5f;
+        BoundBox = new Rectangle(0, 0, 48, 29);
+
+        _anchor = new Vector2(x, y);
+    }
+
+    public override void Draw(SpriteDrawArgs args)
+    {
+        if (TextureName is null)
+            return;
+
+        Texture2D texture = args.Content.Load<Texture2D>(TextureName);
+
+        args.SpriteBatch.Draw(texture, Position, null, DrawColor, 0, new Vector2(0, 0), _scale, SpriteEffects.None, 1);
+    }
+
+    public override void Update(SpriteUpdateContext context)
+    {
+        // Move the anchor using your normal velocities (downward drift)
+        _anchor.Y += YVelocity;
+        _anchor.X += XVelocity;
+
+        // Advance time smoothly (use dt; if you don't have it yet, see note below)
+        float dt = (float)context.GameTime.ElapsedGameTime.TotalSeconds;
+        _t += _omega * dt;
+
+        // Apply circular offset around the anchor
+        XPosition = _anchor.X + MathF.Cos(_t) * _radius;
+        YPosition = _anchor.Y + MathF.Sin(_t) * _radius;
+
+        if (YPosition > context.ViewTransform.ScreenHeight)
+        {
+            IsDead = true;
+            return;
+        }
+
+        base.Update(context);
+    }
+
+    public override void OnCollision(SpriteCollisionContext context)
+    {
+        if (context.Sprite is Player player)
+        {
+            IsDead = true;
+            ApplyEffect(player);
+        }
+    }
+
+    protected abstract void ApplyEffect(Player player);
+}