diff --git a/src/fot.rs b/src/fot.rs
index 68e97ff..caf4488 100644
--- a/src/fot.rs
+++ b/src/fot.rs
@@ -1,4 +1,5 @@
 mod decoder;
+mod entity;
 mod esh;
 mod fstring;
 mod raw;
diff --git a/src/fot/decoder.rs b/src/fot/decoder.rs
index 6e31e59..b91806d 100644
--- a/src/fot/decoder.rs
+++ b/src/fot/decoder.rs
@@ -3,13 +3,15 @@ use anyhow::Result;
 use std::str;
 
 pub trait Decoder: Sized {
-    fn decode(raw: &Raw, offset: usize, size: usize) -> Result<Self>;
+    type Opt;
+    fn decode(raw: &Raw, offset: usize, size: usize, opt: Option<Self::Opt>) -> Result<Self>;
     fn encode(&self) -> Result<Raw>;
     fn get_enc_size(&self) -> usize;
 }
 
 impl Decoder for String {
-    fn decode(raw: &Raw, offset: usize, size: usize) -> Result<Self> {
+    type Opt = ();
+    fn decode(raw: &Raw, offset: usize, size: usize, _: Option<()>) -> Result<Self> {
         let str = &raw.mem[offset..];
         match str.iter().position(|&c| c == 0) {
             Some(pos) => Ok(str::from_utf8(&str[..pos])?.to_string()),
diff --git a/src/fot/entity.rs b/src/fot/entity.rs
new file mode 100644
index 0000000..e69de29
diff --git a/src/fot/esh.rs b/src/fot/esh.rs
index e5c1cee..afda8dc 100644
--- a/src/fot/esh.rs
+++ b/src/fot/esh.rs
@@ -76,7 +76,8 @@ impl ESHValue {
 }
 
 impl Decoder for ESHValue {
-    fn decode(raw: &Raw, offset: usize, _: usize) -> Result<Self> {
+    type Opt = ();
+    fn decode(raw: &Raw, offset: usize, _: usize, _: Option<()>) -> Result<Self> {
         let mut rd = ReadStream::new(raw, offset);
         let data_type = rd.read_u32()?;
         let data_size = rd.read_u32()?;
@@ -248,7 +249,8 @@ pub struct ESH {
 }
 
 impl Decoder for ESH {
-    fn decode(raw: &Raw, offset: usize, _: usize) -> Result<Self> {
+    type Opt = ();
+    fn decode(raw: &Raw, offset: usize, _: usize, _: Option<()>) -> Result<Self> {
         let mut rd = ReadStream::new(raw, offset);
         let tag: Tag = rd.read(0)?;
 
diff --git a/src/fot/fstring.rs b/src/fot/fstring.rs
index 439ba15..25ffc57 100644
--- a/src/fot/fstring.rs
+++ b/src/fot/fstring.rs
@@ -24,7 +24,8 @@ pub struct FString {
 }
 
 impl Decoder for FString {
-    fn decode(raw: &Raw, offset: usize, _: usize) -> Result<Self> {
+    type Opt = ();
+    fn decode(raw: &Raw, offset: usize, _: usize, _: Option<()>) -> Result<Self> {
         let mut rdr = Cursor::new(&raw.mem[offset..]);
         let flen = rdr.read_u32::<LittleEndian>()? as usize;
         let len = flen & !(1 << 31);
diff --git a/src/fot/save.rs b/src/fot/save.rs
index 192adbf..82dd3a3 100644
--- a/src/fot/save.rs
+++ b/src/fot/save.rs
@@ -46,7 +46,7 @@ impl Save {
             return Err(anyhow!("Unable to determine world block size"));
         }
 
-        let world = World::decode(&raw, world_offset, world_size)?;
+        let world = World::decode(&raw, world_offset, world_size, None)?;
         Ok(Save { raw, world })
     }
 
diff --git a/src/fot/sgd.rs b/src/fot/sgd.rs
index 7f5526e..8f27b7f 100644
--- a/src/fot/sgd.rs
+++ b/src/fot/sgd.rs
@@ -15,7 +15,8 @@ pub struct SGD {
 }
 
 impl Decoder for SGD {
-    fn decode(raw: &Raw, offset: usize, _: usize) -> Result<Self> {
+    type Opt = ();
+    fn decode(raw: &Raw, offset: usize, _: usize, _: Option<()>) -> Result<Self> {
         let mut rd = ReadStream::new(raw, offset);
         let tag: Tag = rd.read(0)?;
         let unk1 = rd.read_bytes(0x48)?;
diff --git a/src/fot/ssg.rs b/src/fot/ssg.rs
index 86186fe..e66bb94 100644
--- a/src/fot/ssg.rs
+++ b/src/fot/ssg.rs
@@ -11,7 +11,8 @@ pub struct SSG {
 }
 
 impl Decoder for SSG {
-    fn decode(raw: &Raw, offset: usize, _: usize) -> Result<Self> {
+    type Opt = ();
+    fn decode(raw: &Raw, offset: usize, _: usize, _: Option<()>) -> Result<Self> {
         let mut rd = ReadStream::new(raw, offset);
         let tag: Tag = rd.read(0)?;
         let unk1 = rd.read_bytes(0x14)?;
diff --git a/src/fot/stream.rs b/src/fot/stream.rs
index c85fcba..a7ab63e 100644
--- a/src/fot/stream.rs
+++ b/src/fot/stream.rs
@@ -43,8 +43,17 @@ impl<'a> ReadStream<'a> {
     // "size" is not required to be actual size, it's only
     // a hint for Decoder::decode. Most of the structures are
     // dynamically determining their decoding and encoding sizes
+
+    // read_opt - decode with optional paramters. required for complex structure
+    // with different origins (save / entfile) like entities
+    pub fn read_opt<T: Decoder>(&mut self, size: usize, opt: T::Opt) -> Result<T> {
+        let val = T::decode(&self.raw, self.offset(), size, Some(opt))?;
+        self.skip(val.get_enc_size());
+        Ok(val)
+    }
+
     pub fn read<T: Decoder>(&mut self, size: usize) -> Result<T> {
-        let val = T::decode(&self.raw, self.offset(), size)?;
+        let val = T::decode(&self.raw, self.offset(), size, None)?;
         self.skip(val.get_enc_size());
         Ok(val)
     }
diff --git a/src/fot/tag.rs b/src/fot/tag.rs
index b21e66f..1e9fea9 100644
--- a/src/fot/tag.rs
+++ b/src/fot/tag.rs
@@ -10,7 +10,8 @@ pub struct Tag {
 }
 
 impl Decoder for Tag {
-    fn decode(raw: &Raw, offset: usize, size: usize) -> Result<Self> {
+    type Opt = ();
+    fn decode(raw: &Raw, offset: usize, size: usize, _: Option<()>) -> Result<Self> {
         let mut rd = ReadStream::new(raw, offset);
         let name: String = rd.read(0)?;
         let version: String = rd.read(0)?;
diff --git a/src/fot/world.rs b/src/fot/world.rs
index 6902650..b5fb00d 100644
--- a/src/fot/world.rs
+++ b/src/fot/world.rs
@@ -52,7 +52,13 @@ impl World {
             }
 
             let name = &types[type_idx as usize];
-            println!("offset {:x} idx {} unk1 {} name {}", rd.offset(), i, unk2, name);
+            println!(
+                "offset {:x} idx {} unk1 {} name {}",
+                rd.offset(),
+                i,
+                unk2,
+                name
+            );
             let _: ESH = rd.read(0)?;
         }
 
@@ -61,7 +67,8 @@ impl World {
 }
 
 impl Decoder for World {
-    fn decode(raw: &Raw, offset: usize, size: usize) -> Result<Self> {
+    type Opt = ();
+    fn decode(raw: &Raw, offset: usize, size: usize, _: Option<()>) -> Result<Self> {
         let mut enc = ReadStream::new(raw, offset);
 
         let tag: Tag = enc.read(Self::WORLD_TAG_LEN)?;