The following are new classes added between Maya 2016 and Maya 2016 Extension 2:
OpenMaya
MFnContainerNode
MFnReference
MFnSet
MItDag
MItDependencyGraph
MItDependencyNodes
MIteratorType
MURI
OpenMayaUI
MPaintMessage
MPxDragAndDropBehavior
MPxHardwareShader
ShaderContext
OpenMayaRender
MRenderProfile
MRenderTargetAssignment
MTextureAssignment
MUniformParameter
MUniformParameterList
MVaryingParameter
MVaryingParameterList
MDrawContext