diff --git a/masque/repetition.py b/masque/repetition.py
index 5707a50..5c9f105 100644
--- a/masque/repetition.py
+++ b/masque/repetition.py
@@ -170,8 +170,8 @@ class Grid(LockableImpl, Repetition, metaclass=AutoSlots):
     @property
     def displacements(self) -> numpy.ndarray:
         aa, bb = numpy.meshgrid(numpy.arange(self.a_count), numpy.arange(self.b_count), indexing='ij')
-        return (aa.flat[:, None] * self.a_vector[None, :] +
-                bb.flat[:, None] * self.b_vector[None, :])
+        return (aa.flatten()[:, None] * self.a_vector[None, :] +
+                bb.flatten()[:, None] * self.b_vector[None, :])
 
     def rotate(self, rotation: float) -> 'Grid':
         """
diff --git a/masque/shapes/shape.py b/masque/shapes/shape.py
index c6a0c63..7a5e3f3 100644
--- a/masque/shapes/shape.py
+++ b/masque/shapes/shape.py
@@ -31,16 +31,17 @@ class Shape(PositionableImpl, LayerableImpl, DoseableImpl, Rotatable, Mirrorable
     """
     Abstract class specifying functions common to all shapes.
     """
+    __slots__ = ()      # Children should use AutoSlots
 
     identifier: Tuple
     """ An arbitrary identifier for the shape, usually empty but used by `Pattern.flatten()` """
 
-#    def __copy__(self) -> 'Shape':
-#        cls = self.__class__
-#        new = cls.__new__(cls)
-#        for name in Shape.__slots__ + self.__slots__:
-#            object.__setattr__(new, name, getattr(self, name))
-#        return new
+    def __copy__(self) -> 'Shape':
+        cls = self.__class__
+        new = cls.__new__(cls)
+        for name in self.__slots__:
+            object.__setattr__(new, name, getattr(self, name))
+        return new
 
     '''
     --- Abstract methods
diff --git a/masque/subpattern.py b/masque/subpattern.py
index e898349..6964676 100644
--- a/masque/subpattern.py
+++ b/masque/subpattern.py
@@ -22,7 +22,7 @@ if TYPE_CHECKING:
 
 
 class SubPattern(PositionableImpl, DoseableImpl, RotatableImpl, ScalableImpl, Mirrorable,
-                 Pivotable, Copyable, RepeatableImpl, LockableImpl, metaclass=AutoSlots):
+                 PivotableImpl, Copyable, RepeatableImpl, LockableImpl, metaclass=AutoSlots):
     """
     SubPattern provides basic support for nesting Pattern objects within each other, by adding
      offset, rotation, scaling, and associated methods.
@@ -83,6 +83,7 @@ class SubPattern(PositionableImpl, DoseableImpl, RotatableImpl, ScalableImpl, Mi
                          dose=self.dose,
                          scale=self.scale,
                          mirrored=self.mirrored.copy(),
+                         repetition=copy.deepcopy(self.repetition),
                          locked=self.locked)
         return new
 
@@ -90,6 +91,7 @@ class SubPattern(PositionableImpl, DoseableImpl, RotatableImpl, ScalableImpl, Mi
         memo = {} if memo is None else memo
         new = copy.copy(self).unlock()
         new.pattern = copy.deepcopy(self.pattern, memo)
+        new.repetition = copy.deepcopy(self.repetition, memo)
         new.locked = self.locked
         return new
 
@@ -140,18 +142,17 @@ class SubPattern(PositionableImpl, DoseableImpl, RotatableImpl, ScalableImpl, Mi
 
         return pattern
 
+    def rotate(self, rotation: float) -> 'SubPattern':
+        self.rotation += rotation
+        if self.repetition is not None:
+            self.repetition.rotate(rotation)
+        return self
+
     def mirror(self, axis: int) -> 'SubPattern':
-        """
-        Mirror the subpattern across an axis.
-
-        Args:
-            axis: Axis to mirror across.
-
-        Returns:
-            self
-        """
         self.mirrored[axis] = not self.mirrored[axis]
         self.rotation *= -1
+        if self.repetition is not None:
+            self.repetiton.mirror(axis)
         return self
 
     def get_bounds(self) -> Optional[numpy.ndarray]:
diff --git a/masque/traits/positionable.py b/masque/traits/positionable.py
index 4db6880..d433a91 100644
--- a/masque/traits/positionable.py
+++ b/masque/traits/positionable.py
@@ -94,7 +94,7 @@ class PositionableImpl(Positionable, metaclass=ABCMeta):
 
     @offset.setter
     def offset(self, val: vector2):
-        if not isinstance(val, numpy.ndarray):
+        if not isinstance(val, numpy.ndarray) or val.dtype != numpy.float64:
             val = numpy.array(val, dtype=float)
 
         if val.size != 2:
@@ -109,7 +109,6 @@ class PositionableImpl(Positionable, metaclass=ABCMeta):
         self.offset = offset
         return self
 
-
     def translate(self: I, offset: vector2) -> I:
         self._offset += offset
         return self
diff --git a/masque/traits/rotatable.py b/masque/traits/rotatable.py
index e01c81d..64c2c51 100644
--- a/masque/traits/rotatable.py
+++ b/masque/traits/rotatable.py
@@ -109,6 +109,7 @@ class PivotableImpl(Pivotable, metaclass=ABCMeta):
     """
     __slots__ = ()
 
+    @abstractmethod
     def rotate_around(self: J, pivot: vector2, rotation: float) -> J:
         pivot = numpy.array(pivot, dtype=float)
         self.translate(-pivot)
diff --git a/masque/utils.py b/masque/utils.py
index 979ffde..2f2e499 100644
--- a/masque/utils.py
+++ b/masque/utils.py
@@ -148,11 +148,16 @@ class AutoSlots(ABCMeta):
     can be used to generate a full `__slots__` for the concrete class.
     """
     def __new__(cls, name, bases, dctn):
-        slots = tuple(dctn.get('__slots__', tuple()))
+        parents = set()
         for base in bases:
-            if not hasattr(base, '__annotations__'):
-                continue
-            slots += tuple(getattr(base, '__annotations__').keys())
-        dctn['__slots__'] = slots
-        return super().__new__(cls,name,bases,dctn)
+            parents |= set(base.mro())
+
+        slots = tuple(dctn.get('__slots__', tuple()))
+        for parent in parents:
+            if not hasattr(parent, '__annotations__'):
+                continue
+            slots += tuple(getattr(parent, '__annotations__').keys())
+
+        dctn['__slots__'] = slots
+        return super().__new__(cls, name, bases, dctn)