diff --git a/CMakeLists.txt b/CMakeLists.txt
index 14882a1e..f63e39e9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -163,6 +163,7 @@ add_library(lego1 SHARED
   LEGO1/mxramstreamcontroller.cpp
   LEGO1/mxramstreamprovider.cpp
   LEGO1/mxregion.cpp
+  LEGO1/mxregionlist.cpp
   LEGO1/mxscheduler.cpp
   LEGO1/mxsemaphore.cpp
   LEGO1/mxsmkpresenter.cpp
diff --git a/LEGO1/mxlist.h b/LEGO1/mxlist.h
index f6093f60..ed66f9fc 100644
--- a/LEGO1/mxlist.h
+++ b/LEGO1/mxlist.h
@@ -97,10 +97,15 @@ class MxListCursor : public MxCore {
 
 	MxBool Find(T p_obj);
 	void Detach();
+	void Destroy();
 	MxBool Next(T& p_obj);
+	MxBool Current(T& p_obj);
+	void Advance();
+	MxBool HasMatch() { return m_match != NULL; }
 	void SetValue(T p_obj);
 	void Head() { m_match = m_list->m_first; }
 	void Reset() { m_match = NULL; }
+	void Prepend(T p_newobj);
 
 private:
 	MxList<T>* m_list;
@@ -215,6 +220,12 @@ inline void MxListCursor<T>::Detach()
 	m_match = NULL;
 }
 
+template <class T>
+inline void MxListCursor<T>::Destroy()
+{
+	m_list->m_customDestructor(m_match->GetValue());
+}
+
 template <class T>
 inline MxBool MxListCursor<T>::Next(T& p_obj)
 {
@@ -229,6 +240,24 @@ inline MxBool MxListCursor<T>::Next(T& p_obj)
 	return m_match != NULL;
 }
 
+template <class T>
+inline MxBool MxListCursor<T>::Current(T& p_obj)
+{
+	if (m_match)
+		p_obj = m_match->GetValue();
+
+	return m_match != NULL;
+}
+
+template <class T>
+inline void MxListCursor<T>::Advance()
+{
+	if (!m_match)
+		m_match = m_list->m_first;
+	else
+		m_match = m_match->m_next;
+}
+
 template <class T>
 inline void MxListCursor<T>::SetValue(T p_obj)
 {
@@ -236,4 +265,11 @@ inline void MxListCursor<T>::SetValue(T p_obj)
 		m_match->m_obj = p_obj;
 }
 
+template <class T>
+inline void MxListCursor<T>::Prepend(T p_newobj)
+{
+	if (m_match)
+		m_list->_InsertEntry(p_newobj, m_match->m_prev, m_match);
+}
+
 #endif // MXLIST_H
diff --git a/LEGO1/mxrect32.h b/LEGO1/mxrect32.h
index c3381d46..0ee1bc9c 100644
--- a/LEGO1/mxrect32.h
+++ b/LEGO1/mxrect32.h
@@ -1,6 +1,9 @@
 #ifndef MXRECT32_H
 #define MXRECT32_H
 
+#include "mxpoint32.h"
+#include "mxsize32.h"
+
 class MxRect32 {
 public:
 	MxRect32() {}
@@ -12,14 +15,35 @@ class MxRect32 {
 		this->m_bottom = p_bottom;
 	}
 
+	MxRect32(const MxPoint32& p_point, const MxSize32& p_size)
+	{
+		this->m_left = p_point.m_x;
+		this->m_top = p_point.m_y;
+		this->m_right = p_size.m_width;
+		this->m_bottom = p_size.m_height;
+	}
+
+	inline void SetPoint(const MxPoint32& p_point)
+	{
+		this->m_left = p_point.m_x;
+		this->m_top = p_point.m_y;
+	}
+
+	inline void SetSize(const MxSize32& p_size)
+	{
+		this->m_right = p_size.m_width;
+		this->m_bottom = p_size.m_height;
+	}
+
+	inline MxS32 GetWidth() { return (m_right - m_left) + 1; }
+	inline MxS32 GetHeight() { return (m_bottom - m_top) + 1; }
+
+	inline MxPoint32 GetPoint() { return MxPoint32(this->m_left, this->m_top); }
+
 	MxS32 m_left;
 	MxS32 m_top;
 	MxS32 m_right;
 	MxS32 m_bottom;
-
-	inline MxS32 GetWidth() { return (m_right - m_left) + 1; }
-
-	inline MxS32 GetHeight() { return (m_bottom - m_top) + 1; }
 };
 
 #endif // MXRECT32_H
diff --git a/LEGO1/mxregion.cpp b/LEGO1/mxregion.cpp
index 5b7237cb..bd2a5f5a 100644
--- a/LEGO1/mxregion.cpp
+++ b/LEGO1/mxregion.cpp
@@ -1,40 +1,214 @@
 #include "mxregion.h"
 
-DECOMP_SIZE_ASSERT(MxRegion, 0x1c);
+#include <limits.h>
 
-// OFFSET: LEGO1 0x100c31c0 STUB
+DECOMP_SIZE_ASSERT(MxRegion, 0x1c);
+DECOMP_SIZE_ASSERT(MxRegionTopBottom, 0x0c);
+DECOMP_SIZE_ASSERT(MxRegionLeftRight, 0x08);
+
+// OFFSET: LEGO1 0x100c31c0
 MxRegion::MxRegion()
 {
-	// TODO
+	m_list = new MxRegionList;
+	m_rect.SetPoint(MxPoint32(INT_MAX, INT_MAX));
+	m_rect.SetSize(MxSize32(-1, -1));
 }
 
-// OFFSET: LEGO1 0x100c3690 STUB
-MxRegion::~MxRegion()
-{
-	// TODO
-}
-
-// OFFSET: LEGO1 0x100c3700 STUB
-void MxRegion::Reset()
-{
-	// TODO
-}
-
-// OFFSET: LEGO1 0x100c3750 STUB
-void MxRegion::vtable18(MxRect32& p_rect)
-{
-	// TODO
-}
-
-// OFFSET: LEGO1 0x100c3e20 STUB
-void MxRegion::vtable1c()
-{
-	// TODO
-}
-
-// OFFSET: LEGO1 0x100c3660 STUB
+// OFFSET: LEGO1 0x100c3660
 MxBool MxRegion::vtable20()
 {
-	// TODO
+	return m_list->GetCount() == 0;
+}
+
+// OFFSET: LEGO1 0x100c3690
+MxRegion::~MxRegion()
+{
+	if (m_list)
+		delete m_list;
+}
+
+// OFFSET: LEGO1 0x100c3700
+void MxRegion::Reset()
+{
+	m_list->DeleteAll();
+	m_rect.SetPoint(MxPoint32(INT_MAX, INT_MAX));
+	m_rect.SetSize(MxSize32(-1, -1));
+}
+
+// OFFSET: LEGO1 0x100c3750
+void MxRegion::vtable18(MxRect32& p_rect)
+{
+	MxRect32 rectCopy(p_rect.GetPoint(), MxSize32(p_rect.m_right, p_rect.m_bottom));
+	MxRegionListCursor cursor(m_list);
+
+	if (rectCopy.m_left < rectCopy.m_right) {
+		while (rectCopy.m_top < rectCopy.m_bottom) {
+			MxRegionTopBottom* topBottom;
+			if (!cursor.Next(topBottom))
+				break;
+
+			if (topBottom->m_top >= rectCopy.m_bottom) {
+				cursor.Prepend(new MxRegionTopBottom(rectCopy));
+				rectCopy.m_top = rectCopy.m_bottom;
+			}
+			else if (rectCopy.m_top < topBottom->m_bottom) {
+				if (rectCopy.m_top < topBottom->m_top) {
+					MxRect32 topBottomRect(rectCopy.GetPoint(), MxSize32(rectCopy.m_right, topBottom->m_top));
+
+					cursor.Prepend(new MxRegionTopBottom(topBottomRect));
+					rectCopy.m_top = topBottom->m_top;
+				}
+				else if (topBottom->m_top < rectCopy.m_top) {
+					MxRegionTopBottom* newTopBottom = topBottom->Clone();
+					newTopBottom->m_bottom = rectCopy.m_top;
+					topBottom->m_top = rectCopy.m_top;
+					cursor.Prepend(newTopBottom);
+				}
+
+				if (rectCopy.m_bottom < topBottom->m_bottom) {
+					MxRegionTopBottom* newTopBottom = topBottom->Clone();
+					newTopBottom->m_bottom = rectCopy.m_bottom;
+					topBottom->m_top = rectCopy.m_bottom;
+					newTopBottom->FUN_100c5280(rectCopy.m_left, rectCopy.m_right);
+					// TODO: _InsertEntry currently inlined, shouldn't be
+					cursor.Prepend(newTopBottom);
+					rectCopy.m_top = rectCopy.m_bottom;
+				}
+				else {
+					topBottom->FUN_100c5280(rectCopy.m_left, rectCopy.m_right);
+					rectCopy.m_top = topBottom->m_bottom;
+				}
+			}
+
+			if (rectCopy.m_right <= rectCopy.m_left)
+				break;
+		}
+	}
+
+	if (rectCopy.m_left < rectCopy.m_right && rectCopy.m_top < rectCopy.m_bottom) {
+		MxRegionTopBottom* newTopBottom = new MxRegionTopBottom(rectCopy);
+		m_list->OtherAppend(newTopBottom);
+	}
+
+	m_rect.m_left = m_rect.m_left <= p_rect.m_left ? m_rect.m_left : p_rect.m_left;
+	m_rect.m_top = m_rect.m_top <= p_rect.m_top ? m_rect.m_top : p_rect.m_top;
+	m_rect.m_right = m_rect.m_right <= p_rect.m_right ? p_rect.m_right : m_rect.m_right;
+	m_rect.m_bottom = m_rect.m_bottom <= p_rect.m_bottom ? p_rect.m_bottom : m_rect.m_bottom;
+}
+
+// OFFSET: LEGO1 0x100c3e20
+MxBool MxRegion::vtable1c(MxRect32& p_rect)
+{
+	if (m_rect.m_left >= p_rect.m_right || p_rect.m_left >= m_rect.m_right || m_rect.m_top >= p_rect.m_bottom ||
+		p_rect.m_top >= m_rect.m_bottom)
+		return FALSE;
+
+	MxRegionListCursor cursor(m_list);
+	MxRegionTopBottom* topBottom;
+
+	while (cursor.Next(topBottom)) {
+		if (topBottom->m_top >= p_rect.m_bottom)
+			return FALSE;
+		if (topBottom->m_bottom > p_rect.m_top && topBottom->FUN_100c57b0(p_rect))
+			return TRUE;
+	}
+
+	return FALSE;
+}
+
+// OFFSET: LEGO1 0x100c4c90
+MxRegionTopBottom::MxRegionTopBottom(MxS32 p_top, MxS32 p_bottom)
+{
+	m_top = p_top;
+	m_bottom = p_bottom;
+	m_leftRightList = new MxRegionLeftRightList;
+}
+
+// OFFSET: LEGO1 0x100c50e0
+MxRegionTopBottom::MxRegionTopBottom(MxRect32& p_rect)
+{
+	m_top = p_rect.m_top;
+	m_bottom = p_rect.m_bottom;
+	m_leftRightList = new MxRegionLeftRightList;
+
+	MxRegionLeftRight* leftRight = new MxRegionLeftRight(p_rect.m_left, p_rect.m_right);
+	m_leftRightList->Append(leftRight);
+}
+
+// OFFSET: LEGO1 0x100c5280
+void MxRegionTopBottom::FUN_100c5280(MxS32 p_left, MxS32 p_right)
+{
+	MxRegionLeftRightListCursor a(m_leftRightList);
+	MxRegionLeftRightListCursor b(m_leftRightList);
+
+	MxRegionLeftRight* leftRight;
+	while (a.Next(leftRight) && leftRight->m_right < p_left)
+		;
+
+	if (!a.HasMatch()) {
+		MxRegionLeftRight* copy = new MxRegionLeftRight(p_left, p_right);
+		m_leftRightList->OtherAppend(copy);
+	}
+	else {
+		if (p_left > leftRight->m_left)
+			p_left = leftRight->m_left;
+
+		while (leftRight->m_left < p_right) {
+			if (p_right < leftRight->m_right)
+				p_right = leftRight->m_right;
+
+			// TODO: Currently inlined, shouldn't be
+			b = a;
+			b.Advance();
+
+			if (a.HasMatch()) {
+				a.Destroy();
+				a.Detach();
+			}
+
+			if (!b.Current(leftRight))
+				break;
+
+			a = b;
+		}
+
+		if (a.HasMatch()) {
+			MxRegionLeftRight* copy = new MxRegionLeftRight(p_left, p_right);
+			a.Prepend(copy);
+		}
+		else {
+			MxRegionLeftRight* copy = new MxRegionLeftRight(p_left, p_right);
+			m_leftRightList->OtherAppend(copy);
+		}
+	}
+}
+
+// OFFSET: LEGO1 0x100c55d0
+MxRegionTopBottom* MxRegionTopBottom::Clone()
+{
+	MxRegionTopBottom* clone = new MxRegionTopBottom(m_top, m_bottom);
+
+	MxRegionLeftRightListCursor cursor(m_leftRightList);
+	MxRegionLeftRight* leftRight;
+
+	while (cursor.Next(leftRight))
+		clone->m_leftRightList->Append(leftRight->Clone());
+
+	return clone;
+}
+
+// OFFSET: LEGO1 0x100c57b0
+MxBool MxRegionTopBottom::FUN_100c57b0(MxRect32& p_rect)
+{
+	MxRegionLeftRightListCursor cursor(m_leftRightList);
+	MxRegionLeftRight* leftRight;
+
+	while (cursor.Next(leftRight)) {
+		if (p_rect.m_right <= leftRight->m_left)
+			return FALSE;
+		if (leftRight->m_right > p_rect.m_left)
+			return TRUE;
+	}
+
 	return FALSE;
 }
diff --git a/LEGO1/mxregion.h b/LEGO1/mxregion.h
index 25482207..4317d836 100644
--- a/LEGO1/mxregion.h
+++ b/LEGO1/mxregion.h
@@ -4,6 +4,35 @@
 #include "decomp.h"
 #include "mxcore.h"
 #include "mxrect32.h"
+#include "mxregionlist.h"
+
+// SIZE 0x0c
+struct MxRegionTopBottom {
+	MxRegionTopBottom(MxRect32& p_rect);
+	MxRegionTopBottom(MxS32 m_top, MxS32 m_bottom);
+
+	MxRegionTopBottom* Clone();
+	void FUN_100c5280(MxS32 p_left, MxS32 p_right);
+	MxBool FUN_100c57b0(MxRect32& p_rect);
+
+	MxS32 m_top;
+	MxS32 m_bottom;
+	MxRegionLeftRightList* m_leftRightList;
+};
+
+// SIZE 0x08
+struct MxRegionLeftRight {
+	MxRegionLeftRight(MxS32 p_left, MxS32 p_right)
+	{
+		m_left = p_left;
+		m_right = p_right;
+	}
+
+	MxRegionLeftRight* Clone() { return new MxRegionLeftRight(m_left, m_right); }
+
+	MxS32 m_left;
+	MxS32 m_right;
+};
 
 // VTABLE 0x100dcae8
 // SIZE 0x1c
@@ -14,15 +43,13 @@ class MxRegion : public MxCore {
 
 	virtual void Reset();
 	virtual void vtable18(MxRect32& p_rect);
-	virtual void vtable1c();
+	virtual MxBool vtable1c(MxRect32& p_rect);
 	virtual MxBool vtable20();
 
 	inline MxRect32& GetRect() { return this->m_rect; }
 
 private:
-	// A container (probably MxList) holding MxRect32
-	// MxList<MxRect32*> *m_rects;
-	undefined4 m_unk08;
+	MxRegionList* m_list;
 	MxRect32 m_rect;
 };
 
diff --git a/LEGO1/mxregionlist.cpp b/LEGO1/mxregionlist.cpp
new file mode 100644
index 00000000..a33d78b7
--- /dev/null
+++ b/LEGO1/mxregionlist.cpp
@@ -0,0 +1,19 @@
+#include "mxregionlist.h"
+
+#include "mxregion.h"
+
+// OFFSET: LEGO1 0x100c33e0
+void MxRegionListParent::Destroy(MxRegionTopBottom* p_topBottom)
+{
+	if (p_topBottom) {
+		if (p_topBottom->m_leftRightList)
+			delete p_topBottom->m_leftRightList;
+		delete p_topBottom;
+	}
+}
+
+// OFFSET: LEGO1 0x100c4e80
+void MxRegionLeftRightListParent::Destroy(MxRegionLeftRight* p_leftRight)
+{
+	delete p_leftRight;
+}
diff --git a/LEGO1/mxregionlist.h b/LEGO1/mxregionlist.h
new file mode 100644
index 00000000..52336d38
--- /dev/null
+++ b/LEGO1/mxregionlist.h
@@ -0,0 +1,56 @@
+#ifndef MXREGIONLIST_H
+#define MXREGIONLIST_H
+
+#include "mxlist.h"
+
+struct MxRegionTopBottom;
+struct MxRegionLeftRight;
+
+// VTABLE 0x100dcb40
+// SIZE 0x18
+class MxRegionListParent : public MxList<MxRegionTopBottom*> {
+public:
+	static void Destroy(MxRegionTopBottom* p_topBottom);
+
+	MxRegionListParent() { m_customDestructor = Destroy; }
+};
+
+// VTABLE 0x100dcb58
+// SIZE 0x18
+class MxRegionList : public MxRegionListParent {};
+
+// VTABLE 0x100dcb88
+typedef MxListCursorChildChild<MxRegionTopBottom*> MxRegionListCursor;
+
+// OFFSET: LEGO1 0x100c5970 TEMPLATE
+// MxList<MxRegionTopBottom *>::_InsertEntry
+
+// OFFSET: LEGO1 0x100c5a20 TEMPLATE
+// MxListEntry<MxRegionTopBottom *>::MxListEntry<MxRegionTopBottom *>
+
+// VTABLE 0x100dcc70
+// SIZE 0x18
+class MxRegionLeftRightListParent : public MxList<MxRegionLeftRight*> {
+public:
+	static void Destroy(MxRegionLeftRight* p_leftRight);
+
+	MxRegionLeftRightListParent() { m_customDestructor = Destroy; }
+};
+
+// VTABLE 0x100dcc88
+// SIZE 0x18
+class MxRegionLeftRightList : public MxRegionLeftRightListParent {};
+
+// VTABLE 0x100dcc10
+typedef MxListCursorChildChild<MxRegionLeftRight*> MxRegionLeftRightListCursor;
+
+// OFFSET: LEGO1 0x100c54f0 TEMPLATE
+// MxListCursor<MxRegionLeftRight *>::MxListCursor<MxRegionLeftRight *>
+
+// OFFSET: LEGO1 0x100c58c0 TEMPLATE
+// MxList<MxRegionLeftRight *>::_InsertEntry
+
+// OFFSET: LEGO1 0x100c5a40 TEMPLATE
+// MxList<MxRegionLeftRight *>::_DeleteEntry
+
+#endif // MXREGIONLIST_H
diff --git a/LEGO1/mxsize32.h b/LEGO1/mxsize32.h
new file mode 100644
index 00000000..a55326cc
--- /dev/null
+++ b/LEGO1/mxsize32.h
@@ -0,0 +1,19 @@
+#ifndef MXSIZE32_H
+#define MXSIZE32_H
+
+#include "mxtypes.h"
+
+class MxSize32 {
+public:
+	MxSize32() {}
+	MxSize32(MxS32 p_width, MxS32 p_height)
+	{
+		this->m_width = p_width;
+		this->m_height = p_height;
+	}
+
+	MxS32 m_width;
+	MxS32 m_height;
+};
+
+#endif // MXSIZE32_H