ah

src/main/java/dev/tggamesyt/szar/Szar.java

@@ -647,6 +647,11 @@ public class Szar implements ModInitializer {
                             })
             );
         });
+        Registry.register(
+                Registries.ITEM,
+                new Identifier(MOD_ID, "towers"),
+                new BlockItem(OBELISK_CORE, new Item.Settings())
+        );
     }
     public static final StructurePieceType TNT_OBELISK_PIECE =
             Registry.register(

src/main/resources/assets/szar/lang/en_us.json

@@ -72,5 +72,6 @@
   "entity.szar.merl": "Merl",
   "item.szar.merl_spawn_egg": "Merl Spawn Egg",
   "effect.szar.pregnant": "Pregnant",
-  "entity.szar.kid": "Kid"
+  "entity.szar.kid": "Kid",
+  "block.szar.obelisk_core": "Towers Core Block"
 }

src/main/resources/assets/szar/models/item/towers.json

@@ -0,0 +1,6 @@
+{
+  "parent": "minecraft:item/generated",
+  "textures": {
+    "layer0": "szar:item/towers"
+  }
+}

src/main/resources/data/szar/advancements/two_towers_explosion.json

@@ -5,7 +5,7 @@
     }
   },
   "display": {
-    "icon": { "item": "minecraft:tnt" },
+    "icon": { "item": "szar:towers" },
     "title": "Hmm, familiar...",
     "description": "You were there when the towers fell",
     "frame": "challenge",