diff --git a/source/MobSpawner.cpp b/source/MobSpawner.cpp
new file mode 100644
index 000000000..19e3739cd
--- /dev/null
+++ b/source/MobSpawner.cpp
@@ -0,0 +1,277 @@
+
+#include "Globals.h"  // NOTE: MSVC stupidness requires this to be the same across all modules
+
+#include "MobSpawner.h"
+#include "MobTypesManager.h"
+#include "Mobs/Monster.h"
+#include "Mobs/IncludeAllMonsters.h"
+
+
+cMobSpawner::tMobTypes& cMobSpawner::m_MobTypes()
+{
+	static tMobTypes* value = new tMobTypes(initMobTypesBeforeCx11());
+	return *value;
+}
+
+cMobSpawner::tMobTypes cMobSpawner::initMobTypesBeforeCx11()
+{
+	std::set<cMonster::eType> toReturn;
+	toReturn.insert(cMonster::mtCreeper);
+	toReturn.insert(cMonster::mtSkeleton);
+	toReturn.insert(cMonster::mtSpider);
+	toReturn.insert(cMonster::mtGiant);
+	toReturn.insert(cMonster::mtZombie);
+	toReturn.insert(cMonster::mtSlime);
+	toReturn.insert(cMonster::mtGhast);
+	toReturn.insert(cMonster::mtZombiePigman);
+	toReturn.insert(cMonster::mtEnderman);
+	toReturn.insert(cMonster::mtCaveSpider);
+	toReturn.insert(cMonster::mtSilverfish);
+	toReturn.insert(cMonster::mtBlaze);
+	toReturn.insert(cMonster::mtMagmaCube);
+	toReturn.insert(cMonster::mtEnderDragon);
+	toReturn.insert(cMonster::mtWither);
+	toReturn.insert(cMonster::mtBat);
+	toReturn.insert(cMonster::mtWitch);
+	toReturn.insert(cMonster::mtPig);
+	toReturn.insert(cMonster::mtSheep);
+	toReturn.insert(cMonster::mtCow);
+	toReturn.insert(cMonster::mtChicken);
+	toReturn.insert(cMonster::mtSquid);
+	toReturn.insert(cMonster::mtWolf);
+	toReturn.insert(cMonster::mtMooshroom);
+	toReturn.insert(cMonster::mtSnowGolem);
+	toReturn.insert(cMonster::mtOcelot);
+	toReturn.insert(cMonster::mtIronGolem);
+	toReturn.insert(cMonster::mtVillager);
+	return toReturn;
+}
+
+
+cMobSpawner::cMobSpawner(cMonster::eFamily a_MonsterFamily,const std::set<cMonster::eType>& a_AllowedTypes) :
+	m_MonsterFamily(a_MonsterFamily),
+	m_NewPack(true),
+	m_MobType(cMonster::mtInvalidType)
+{
+	for (std::set<cMonster::eType>::const_iterator itr = a_AllowedTypes.begin(); itr != a_AllowedTypes.end(); itr++)
+	{
+		if (cMobTypesManager::getFamilyFromType(*itr) == a_MonsterFamily)
+		{
+			m_AllowedTypes.insert(*itr);
+		}
+	}
+}
+
+bool cMobSpawner::CheckPackCenter(BLOCKTYPE a_BlockType)
+{
+	// Packs of non-water mobs can only be centered on an air block
+	// Packs of water mobs can only be centered on a water block
+	if (m_MonsterFamily == cMonster::mfWater)
+	{
+		return IsBlockWater(a_BlockType);
+	}
+	else
+	{
+		return a_BlockType == E_BLOCK_AIR;
+	}
+}
+
+void cMobSpawner::addIfAllowed(cMonster::eType toAdd, std::set<cMonster::eType>& toAddIn)
+{
+	std::set<cMonster::eType>::iterator itr = m_AllowedTypes.find(toAdd);
+	if (itr != m_AllowedTypes.end())
+	{
+		toAddIn.insert(toAdd);
+	}
+}
+
+cMonster::eType cMobSpawner::ChooseMobType(EMCSBiome a_Biome)
+{
+	std::set<cMonster::eType> allowedMobs;
+
+	if (a_Biome == biMushroomIsland || a_Biome == biMushroomShore)
+	{
+		addIfAllowed(cMonster::mtMooshroom, allowedMobs);
+	}
+	else if (a_Biome == biNether)
+	{
+		addIfAllowed(cMonster::mtGhast, allowedMobs);
+		addIfAllowed(cMonster::mtZombiePigman, allowedMobs);
+		addIfAllowed(cMonster::mtMagmaCube, allowedMobs);
+	}
+	/*else if (a_Biome == biEnder)	MG TODO : figure out what are the biomes of the ender
+	{
+		addIfAllowed(cMonster::mtEnderman, allowedMobs);
+	}*/
+	else
+	{
+		addIfAllowed(cMonster::mtBat, allowedMobs);
+		addIfAllowed(cMonster::mtSpider, allowedMobs);
+		addIfAllowed(cMonster::mtZombie, allowedMobs);
+		addIfAllowed(cMonster::mtSkeleton, allowedMobs);
+		addIfAllowed(cMonster::mtCreeper, allowedMobs);
+		addIfAllowed(cMonster::mtSquid, allowedMobs);
+		
+		if (a_Biome != biDesert && a_Biome != biBeach && a_Biome != biOcean)
+		{
+			addIfAllowed(cMonster::mtSheep, allowedMobs);
+			addIfAllowed(cMonster::mtPig, allowedMobs);
+			addIfAllowed(cMonster::mtCow, allowedMobs);
+			addIfAllowed(cMonster::mtChicken, allowedMobs);
+			addIfAllowed(cMonster::mtEnderman, allowedMobs);
+			addIfAllowed(cMonster::mtSlime, allowedMobs);	// MG TODO : much more complicated rule
+			
+			if (a_Biome == biForest || a_Biome == biForestHills || a_Biome == biTaiga  || a_Biome == biTaigaHills)
+			{
+				addIfAllowed(cMonster::mtWolf, allowedMobs);
+			}
+			else if (a_Biome == biJungle || a_Biome == biJungleHills)
+			{
+				addIfAllowed(cMonster::mtOcelot, allowedMobs);
+			}
+		}
+	}
+
+	int allowedMobsSize = allowedMobs.size();
+	if (allowedMobsSize > 0)
+	{
+		std::set<cMonster::eType>::iterator itr = allowedMobs.begin();
+		int iRandom = m_Random.NextInt(allowedMobsSize,a_Biome);
+
+		for(int i = 0; i < iRandom; i++)
+		{
+			itr++;
+		}
+
+		return *itr;
+	}
+	return cMonster::mtInvalidType;
+}
+
+
+bool cMobSpawner::CanSpawnHere(cMonster::eType a_MobType, BLOCKTYPE a_BlockType, NIBBLETYPE a_BlockMeta, BLOCKTYPE a_BlockType_below, NIBBLETYPE a_BlockMeta_below, BLOCKTYPE a_BlockType_above, NIBBLETYPE a_BlockMeta_above, EMCSBiome a_Biome, int a_Level)
+{
+	bool toReturn = false;
+	std::set<cMonster::eType>::iterator itr = m_AllowedTypes.find(a_MobType);
+	if (itr != m_AllowedTypes.end())
+	{
+		// MG TODO : find a nicer paging
+		if (a_MobType == cMonster::mtSquid)
+		{
+			toReturn = (
+				IsBlockLiquid(a_BlockType) &&
+				a_Level >= 45 &&
+				a_Level <= 62
+			);
+		}
+		else if (a_MobType == cMonster::mtBat)
+		{
+			toReturn = a_Level <= 60; // MG TODO  : find a real rule
+		}
+		else
+		{
+			if (
+				a_BlockType == E_BLOCK_AIR &&
+				a_BlockType_above == E_BLOCK_AIR &&
+				! (g_BlockTransparent[a_BlockType_below])
+				)
+			{
+				if (a_MobType == cMonster::mtChicken || a_MobType == cMonster::mtPig || a_MobType == cMonster::mtCow || a_MobType == cMonster::mtSheep)
+				{
+					LOGD("Trying to spawn an animal");
+					toReturn = (
+						a_BlockType_below == E_BLOCK_GRASS /*&& // MG TODO
+						a_LightLevel >= 9 */
+						);
+				}
+				else if (a_MobType == cMonster::mtOcelot)
+				{
+					toReturn = (
+						a_Level >= 62 &&
+						(
+							a_BlockType_below == E_BLOCK_GRASS ||
+							a_BlockType_below == E_BLOCK_LEAVES
+						) &&
+						m_Random.NextInt(3,a_Biome) != 0
+						);
+				}
+				else if (a_MobType == cMonster::mtCreeper || a_MobType == cMonster::mtSkeleton || a_MobType == cMonster::mtZombie || a_MobType == cMonster::mtSpider || a_MobType == cMonster::mtEnderman || a_MobType == cMonster::mtZombiePigman)
+				{
+					toReturn = true /*a_LightLevel <= 7 MG TODO*/;
+					/*if (a_SunLight) MG TODO 
+					{
+						if (m_Random.NextInt(2,a_Biome) != 0)
+						{
+							toReturn = false;
+						}
+					}*/
+				}
+				else if (a_MobType == cMonster::mtSlime)
+				{
+					toReturn = a_Level <= 40;
+					// MG TODO : much more complicated rules		
+				}
+				else if (a_MobType == cMonster::mtGhast)
+				{
+					toReturn = m_Random.NextInt(20,a_Biome) == 0;
+				}
+				else
+				{
+					LOGD("MG TODO : check I've got a Rule to write for type %d",a_MobType);
+					toReturn = true;
+				}
+			}
+		}
+	}
+	return toReturn;
+}
+
+
+cMonster* cMobSpawner::TryToSpawnHere(BLOCKTYPE a_BlockType, NIBBLETYPE a_BlockMeta, BLOCKTYPE a_BlockType_below, NIBBLETYPE a_BlockMeta_below, BLOCKTYPE a_BlockType_above, NIBBLETYPE a_BlockMeta_above, EMCSBiome a_Biome, int a_Level, int& a_MaxPackSize)
+{
+	cMonster* toReturn = NULL;
+	if (m_NewPack)
+	{
+		m_MobType = ChooseMobType(a_Biome);
+		if (m_MobType == cMonster::mtInvalidType)
+		{
+			return toReturn;
+		}
+		if (m_MobType == cMonster::mtWolf)
+		{
+			a_MaxPackSize = 8;
+		}
+		else if (m_MobType == cMonster::mtGhast)
+		{
+			a_MaxPackSize = 1;
+		}
+		m_NewPack = false;
+	}
+
+	
+	if (CanSpawnHere(m_MobType, a_BlockType, a_BlockMeta, a_BlockType_below, a_BlockMeta_below, a_BlockType_above, a_BlockMeta_above, a_Biome, a_Level))
+	{
+		cMonster* newMob = cMobTypesManager::NewMonsterFromType(m_MobType);
+		if (newMob)
+		{
+			m_Spawned.insert(newMob);
+		}
+		toReturn = newMob;
+	}
+	return toReturn;
+}
+
+void cMobSpawner::NewPack()
+{
+	m_NewPack = true;
+}
+
+cMobSpawner::tSpawnedContainer& cMobSpawner::getSpawned()
+{
+	return m_Spawned;
+}
+
+bool cMobSpawner::CanSpawnSomething()
+{
+	return m_AllowedTypes.size() > 0;
+}
diff --git a/source/MobSpawner.h b/source/MobSpawner.h
index 7498c567d..bb9e95172 100644
--- a/source/MobSpawner.h
+++ b/source/MobSpawner.h
@@ -8,7 +8,6 @@
 #include "Mobs/Monster.h" //this is a side-effect of keeping Mobfamily inside Monster class. I'd prefer to keep both (Mobfamily and Monster) inside a "Monster" namespace MG TODO : do it
 
 class cChunk;
-class cEntity;
 
 
 // This class is used to determine wich monster can be spawned on wich place
@@ -18,11 +17,56 @@ class cMobSpawner
 {
 public :
 	// constructor
-	// a_MobFamily is the mega type of mobs that this spawner will spawn
+	// a_MobFamily is the Family of mobs that this spawner will spawn
 	// a_AllowedTypes is the set of types allowed for mobs it will spawn. Empty set
 	// would result in no spawn at all
-	// Allowed mobs thah are not of the right Megatype will not be include (no warning)
+	// Allowed mobs thah are not of the right Family will not be include (no warning)
 	cMobSpawner(cMonster::eFamily MobFamily, const std::set<cMonster::eType>& a_AllowedTypes);
 
+	// Check if specified block can be a Pack center for this spawner
+	bool CheckPackCenter(BLOCKTYPE a_BlockType);
+
+	// Try to create a monster here
+	// if this is the first of a Pack : determine the type of monster
+	// BlockType & BlockMeta are use to know what kind of Mob can Spawn here
+	// MaxPackSize is set to the maximal size for a pack this type of mob
+	cMonster* TryToSpawnHere(BLOCKTYPE a_BlockType, NIBBLETYPE a_BlockMeta, BLOCKTYPE a_BlockType_below, NIBBLETYPE a_BlockMeta_below, BLOCKTYPE a_BlockType_above, NIBBLETYPE a_BlockMeta_above, EMCSBiome a_Biome, int a_Level, int& a_MaxPackSize);
+
+	// mark the beginning of a new Pack
+	// all mobs of the same Pack are the same type
+	void NewPack();
+
+	// return true if there is at least one allowed type
+	bool CanSpawnSomething();
+
+	typedef const std::set<cMonster*> tSpawnedContainer;
+	tSpawnedContainer& getSpawned();
+
+protected : 
+	// return true if specified type of mob can spawn on specified block
+	bool CanSpawnHere(cMonster::eType a_MobType, BLOCKTYPE a_BlockType, NIBBLETYPE a_BlockMeta, BLOCKTYPE a_BlockType_below, NIBBLETYPE a_BlockMeta_below, BLOCKTYPE a_BlockType_above, NIBBLETYPE a_BlockMeta_above, EMCSBiome a_Biome, int a_Level);
+
+	// return a random type that can spawn on specified biome.
+	// returns E_ENTITY_TYPE_DONOTUSE if none is possible
+	cMonster::eType ChooseMobType(EMCSBiome a_Biome);
+
+	// add toAdd inside toAddIn, if toAdd is in m_AllowedTypes
+	void addIfAllowed(cMonster::eType toAdd, std::set<cMonster::eType>& toAddIn);
+
+protected : 
+	cMonster::eFamily m_MonsterFamily;
+	std::set<cMonster::eType> m_AllowedTypes;
+	bool m_NewPack;
+	cMonster::eType m_MobType;
+	std::set<cMonster*> m_Spawned;
+	cFastRandom m_Random;
+
+public : 
+	typedef const std::set<cMonster::eType> tMobTypes; // MG TODO : maybe relocate all those statics set/maps in the same place ?
+	static tMobTypes& m_MobTypes();
+
+protected : 
+	static tMobTypes initMobTypesBeforeCx11();
+
 
 };
diff --git a/source/MobTypesManager.cpp b/source/MobTypesManager.cpp
index d8606e619..0c13e5aea 100644
--- a/source/MobTypesManager.cpp
+++ b/source/MobTypesManager.cpp
@@ -44,6 +44,43 @@ cMobTypesManager::tMobTypes2Names cMobTypesManager::MobTypes2NamesInitializerBef
 	return toReturn;
 }
 
+cMobTypesManager::tMobType2Family& cMobTypesManager::m_MobsType2Family()
+{
+	static std::map<cMonster::eType,cMonster::eFamily>* value = new std::map<cMonster::eType,cMonster::eFamily>(MobType2FamilyInitializerBeforeCx11());
+	return *value;
+}
+
+cMobTypesManager::tMobType2Family cMobTypesManager::MobType2FamilyInitializerBeforeCx11()
+{
+	std::map<cMonster::eType,cMonster::eFamily> toReturn;
+	typedef std::map<cMonster::eType,cMonster::eFamily>::value_type ValueType;
+	toReturn.insert(ValueType(cMonster::mtBat,cMonster::mfAmbient));
+	toReturn.insert(ValueType(cMonster::mtSquid,cMonster::mfWater));
+	toReturn.insert(ValueType(cMonster::mtCow,cMonster::mfPassive));
+	toReturn.insert(ValueType(cMonster::mtPig,cMonster::mfPassive));
+	toReturn.insert(ValueType(cMonster::mtSheep,cMonster::mfPassive));
+	toReturn.insert(ValueType(cMonster::mtChicken,cMonster::mfPassive));
+	toReturn.insert(ValueType(cMonster::mtVillager,cMonster::mfPassive));
+	toReturn.insert(ValueType(cMonster::mtMagmaCube,cMonster::mfHostile));
+	toReturn.insert(ValueType(cMonster::mtSlime,cMonster::mfHostile));
+	toReturn.insert(ValueType(cMonster::mtBlaze,cMonster::mfHostile));
+	toReturn.insert(ValueType(cMonster::mtCaveSpider,cMonster::mfHostile));
+	toReturn.insert(ValueType(cMonster::mtCreeper,cMonster::mfHostile));
+	toReturn.insert(ValueType(cMonster::mtEnderman,cMonster::mfHostile));
+	toReturn.insert(ValueType(cMonster::mtGhast,cMonster::mfHostile));
+	toReturn.insert(ValueType(cMonster::mtMooshroom,cMonster::mfHostile));
+	toReturn.insert(ValueType(cMonster::mtOcelot,cMonster::mfHostile));
+	toReturn.insert(ValueType(cMonster::mtSilverfish,cMonster::mfHostile));
+	toReturn.insert(ValueType(cMonster::mtSkeleton,cMonster::mfHostile));
+	toReturn.insert(ValueType(cMonster::mtSpider,cMonster::mfHostile));
+	toReturn.insert(ValueType(cMonster::mtWitch,cMonster::mfHostile));
+	toReturn.insert(ValueType(cMonster::mtWolf,cMonster::mfHostile));
+	toReturn.insert(ValueType(cMonster::mtZombie,cMonster::mfHostile));
+	toReturn.insert(ValueType(cMonster::mtZombiePigman,cMonster::mfHostile));	
+
+	return toReturn;
+}
+
 
 cFastRandom& cMobTypesManager::m_Random()
 {
@@ -126,5 +163,16 @@ cMonster::eType cMobTypesManager::fromStringToMobType(const std::string& a_Name)
 			return itr->first;			
 		}
 	}
-	throw new NotAMonsterException();
+	return cMonster::mtInvalidType;
+}
+
+cMonster::eFamily cMobTypesManager::getFamilyFromType(cMonster::eType a_Type)
+{
+	cMonster::eFamily toReturn = cMonster::mfMaxplusone;
+	std::map<cMonster::eType,cMonster::eFamily>::const_iterator itr = m_MobsType2Family().find(a_Type);
+	if (itr != m_MobsType2Family().end())
+	{
+		toReturn = itr->second;
+	}
+	return toReturn;
 }
diff --git a/source/MobTypesManager.h b/source/MobTypesManager.h
index 0e628899e..a1b2dfddc 100644
--- a/source/MobTypesManager.h
+++ b/source/MobTypesManager.h
@@ -10,20 +10,23 @@ class cFastRandom;
 // functionnalities are (in the first version) :
 // - create a mob from its type (as enum) (in that way it is a compiler-proxy for mobs)
 // - can transform MobTypes from enums to string and reciprocal
+// - return mob family from providen type
 class cMobTypesManager
 {
 public:
 	static const std::string& fromMobTypeToString(cMonster::eType a_MobType);
-	static cMonster::eType fromStringToMobType(const std::string&);
-
-public:
-	class NotAMonsterException : public std::exception {}; //MG TODO : check if this is this project way to do it
+	static cMonster::eType fromStringToMobType(const std::string& a_MobTypeName);
+	static cMonster::eFamily getFamilyFromType(cMonster::eType a_MobType);
 
 protected : 
 	typedef const std::map<cMonster::eType,std::string> tMobTypes2Names;
 	static tMobTypes2Names& m_MobsTypes2Names();
 	static tMobTypes2Names MobTypes2NamesInitializerBeforeCx11();
 
+	typedef const std::map<cMonster::eType,cMonster::eFamily> tMobType2Family;  //MG TODO : this is redundancy with cMonster::getFamily() methods. But almost all the management of MobType is redundancy in this project. Maybe is it optimization, or just historical TODO : understand and do something about it.
+	static tMobType2Family& m_MobsType2Family();
+	static tMobType2Family MobType2FamilyInitializerBeforeCx11();
+
 	static cFastRandom& m_Random();
 	
 public :
diff --git a/source/Mobs/Monster.h b/source/Mobs/Monster.h
index 594914ca0..ef7904e8e 100644
--- a/source/Mobs/Monster.h
+++ b/source/Mobs/Monster.h
@@ -54,6 +54,8 @@ public:
 		mtOcelot       = E_META_SPAWN_EGG_OCELOT,
 		mtIronGolem    = E_META_SPAWN_EGG_IRON_GOLEM,
 		mtVillager     = E_META_SPAWN_EGG_VILLAGER,
+
+		mtInvalidType,  // MG TODO : be sure this is the way we do in this project. (needed inside cMobSpawner::ChooscMonster for instance if nothing can be spawned)
 	} ;
 
 	enum eFamily
@@ -62,7 +64,8 @@ public:
 		mfPassive  = 1, // Cows, Pigs
 		mfAmbient  = 2, // Bats
 		mfWater    = 3, // Squid
-		mfMaxplusone = 4, // Nothing
+
+		mfMaxplusone, // Nothing. Be sure this is the last and the others are in order
 	} ;
 	
 	// tolua_end