Sprites for custom Things can be supplied with a "#$Sprite" comment.

Source/Core/Config/ThingTypeInfo.cs

@@ -412,7 +412,7 @@ namespace CodeImp.DoomBuilder.Config
             for (int i = 0; i < Linedef.NUM_ARGS; i++) this.args[i] = new ArgumentInfo(i);
 
             // Read properties
-            this.sprite = cat.Sprite;
+            this.sprite = o.sprite;
             this.color = cat.Color;
             this.alpha = cat.Alpha; //mxd
             this.alphabyte = (byte)(this.alpha * 255); //mxd

Source/Core/SRB2/SOCObjectParser.cs

@@ -6,6 +6,7 @@ using System.Globalization;
 using System.IO;
 using System.Text;
 using CodeImp.DoomBuilder.Compilers;
+using CodeImp.DoomBuilder.Data;
 using CodeImp.DoomBuilder.ZDoom;
 using CodeImp.DoomBuilder.GZBuilder.Data;
 
@@ -137,6 +138,7 @@ namespace CodeImp.DoomBuilder.SRB2
         private bool ParseObject(string name)
         {
             if (name == null) return false;
+            string sprite = DataManager.INTERNAL_PREFIX + "unknownthing";
             string[] states = new string[8];
             int mapThingNum = -1;
             int radius = 0;
@@ -146,6 +148,11 @@ namespace CodeImp.DoomBuilder.SRB2
                 string line = streamreader.ReadLine();
                 linenumber++;
                 if (String.IsNullOrEmpty(line) || line.StartsWith("\n")) break;
+                if (line.StartsWith("#$Sprite "))
+                {
+                    sprite = line.Substring(9);
+                    continue;
+                }
                 if (line.StartsWith("#")) continue;
                 line = RemoveComments(line);
                 string[] tokens = line.Split(new char[] { '=' });
@@ -210,7 +217,7 @@ namespace CodeImp.DoomBuilder.SRB2
             }
             if (mapThingNum > 0)
             {
-                SRB2Object o = new SRB2Object(name, states, mapThingNum, radius, height);
+                SRB2Object o = new SRB2Object(name, sprite, states, mapThingNum, radius, height);
                 if (objects.ContainsKey(name))
                     objects[name] = o;
                 else

Source/Core/SRB2/SRB2Object.cs

@@ -33,6 +33,7 @@ namespace CodeImp.DoomBuilder.SRB2
 		#region ================== Variables
 		
 		public readonly string name;
+        public readonly string sprite;
         public readonly string[] states;
         public readonly int mapThingNum;
         public readonly int radius;
@@ -43,9 +44,10 @@ namespace CodeImp.DoomBuilder.SRB2
 		#region ================== Constructor / Disposer
 		
 		// Constructor
-		internal SRB2Object(string name, string[] states, int mapThingNum, int radius, int height)
+		internal SRB2Object(string name, string sprite, string[] states, int mapThingNum, int radius, int height)
 		{
             this.name = name;
+            this.sprite = sprite;
             this.states = states;
             this.mapThingNum = mapThingNum;
             this.radius = radius;