diff --git a/TechbloxModdingAPI/Block.cs b/TechbloxModdingAPI/Block.cs
index 1b1cd23..c76ee08 100644
--- a/TechbloxModdingAPI/Block.cs
+++ b/TechbloxModdingAPI/Block.cs
@@ -67,7 +67,7 @@ namespace TechbloxModdingAPI
 		/// <returns>The block object or null if doesn't exist</returns>
 		public static Block GetLastPlacedBlock()
 		{
-			uint lastBlockID = (uint) AccessTools.Field(typeof(CommonExclusiveGroups), "_nextBlockEntityID").GetValue(null) - 1;
+			uint lastBlockID = CommonExclusiveGroups.blockIDGeneratorClient.Peek() - 1;
 			EGID? egid = BlockEngine.FindBlockEGID(lastBlockID);
 			return egid.HasValue ? New(egid.Value) : null;
 		}
@@ -366,8 +366,12 @@ namespace TechbloxModdingAPI
 			get
 			{
 				if (blockGroup != null) return blockGroup;
+				if (!GameState.IsBuildMode()) return null; // Breaks in simulation
 				var bgec = BlockEngine.GetBlockInfo<BlockGroupEntityComponent>(this);
-				return blockGroup = bgec.currentBlockGroup == -1 ? null : new BlockGroup(bgec.currentBlockGroup, this);
+				return blockGroup = bgec.currentBlockGroup == -1
+					? null
+					: GetInstance(new EGID((uint)bgec.currentBlockGroup, BlockGroupExclusiveGroups.BlockGroupEntityGroup),
+						egid => new BlockGroup((int)egid.entityID, this));
 			}
 			set
 			{
@@ -395,6 +399,23 @@ namespace TechbloxModdingAPI
 			set => BlockEngine.GetBlockInfo<BlockStaticComponent>(this).isStatic = value;
 		}
 
+		/// <summary>
+		/// The mass of the block.
+		/// </summary>
+		public float Mass
+		{
+			get => BlockEngine.GetBlockInfo<MassStruct>(this).mass;
+		}
+
+		/// <summary>
+		/// Block complexity used for build rules. Determines the 'cost' of the block.
+		/// </summary>
+		public BlockComplexity Complexity
+		{
+			get => new(BlockEngine.GetBlockInfo<BlockComplexityComponent>(this));
+			set => BlockEngine.GetBlockInfo<BlockComplexityComponent>(this) = value;
+		}
+
 		/// <summary>
 		/// Whether the block exists. The other properties will return a default value if the block doesn't exist.
 		/// If the block was just placed, then this will also return false but the properties will work correctly.
diff --git a/TechbloxModdingAPI/Blocks/BlockComplexity.cs b/TechbloxModdingAPI/Blocks/BlockComplexity.cs
new file mode 100644
index 0000000..9f32866
--- /dev/null
+++ b/TechbloxModdingAPI/Blocks/BlockComplexity.cs
@@ -0,0 +1,17 @@
+using RobocraftX.Blocks;
+
+namespace TechbloxModdingAPI.Blocks
+{
+    public record BlockComplexity(int Cpu, int Power)
+    {
+        public BlockComplexity(BlockComplexityComponent component) : this(component.cpu, component.power)
+        {
+        }
+
+        public int Cpu { get; } = Cpu;
+        public int Power { get; } = Power;
+
+        public static implicit operator BlockComplexityComponent(BlockComplexity complexity) =>
+            new() { cpu = complexity.Cpu, power = complexity.Power };
+    }
+}
\ No newline at end of file
diff --git a/TechbloxModdingAPI/Cluster.cs b/TechbloxModdingAPI/Cluster.cs
index f88cec9..79eb7b9 100644
--- a/TechbloxModdingAPI/Cluster.cs
+++ b/TechbloxModdingAPI/Cluster.cs
@@ -1,6 +1,7 @@
 using Gamecraft.Damage;
 using RobocraftX.Common;
 using Svelto.ECS;
+using Techblox.Physics;
 
 namespace TechbloxModdingAPI
 {
@@ -36,6 +37,11 @@ namespace TechbloxModdingAPI
             set => Block.BlockEngine.GetBlockInfo<HealthEntityComponent>(this).healthMultiplier = value;
         }
 
+        /// <summary>
+        /// The mass of the cluster.
+        /// </summary>
+        public float Mass => Block.BlockEngine.GetBlockInfo<ClusterMassComponent>(this).mass;
+
         /// <summary>
         /// Returns the simulation-time rigid bodies for the chunks in this cluster.
         /// </summary>
diff --git a/TechbloxModdingAPI/Player.cs b/TechbloxModdingAPI/Player.cs
index 68f5e49..a535269 100644
--- a/TechbloxModdingAPI/Player.cs
+++ b/TechbloxModdingAPI/Player.cs
@@ -66,13 +66,16 @@ namespace TechbloxModdingAPI
 
         /// <summary>
         /// Returns the current player belonging to this client. It will be different after entering/leaving simulation.
+        /// May return null if the local player doesn't exist.
         /// </summary>
         public static Player LocalPlayer
         {
 	        get
 	        {
-		        if (localPlayer == null || localPlayer.Id != playerEngine.GetLocalPlayer())
-			        localPlayer = GetInstance(playerEngine.GetLocalPlayer());
+		        var playerId = playerEngine.GetLocalPlayer();
+		        if (playerId == uint.MaxValue) return null;
+		        if (localPlayer == null || localPlayer.Id != playerId)
+			        localPlayer = GetInstance(playerId);
 		        return localPlayer;
 	        }
         }
diff --git a/TechbloxModdingAPI/SimBody.cs b/TechbloxModdingAPI/SimBody.cs
index bb05005..158927a 100644
--- a/TechbloxModdingAPI/SimBody.cs
+++ b/TechbloxModdingAPI/SimBody.cs
@@ -75,13 +75,13 @@ namespace TechbloxModdingAPI
 
         public float Mass
         {
-            get => math.rcp(GetStruct().physicsMass.InverseMass);
+            get => 0f; //TODO: Get mass from UECS entity
             //set => GetStruct().physicsMass.InverseMass = math.rcp(value);
         }
 
         public float3 CenterOfMass
         {
-            get => GetStruct().physicsMass.CenterOfMass;
+            get => Block.BlockEngine.GetBlockInfo<MassEntityStruct>(this).centreOfMass;
             //set => GetStruct().physicsMass.CenterOfMass = value;
         }