DSP Emulator engine to DSP HLE Emulation (fast, but you may encounter audio glitches, if so, you may want to switch to DSP LLE Recompiler which is slower but more accurate).Reduce detail in your graphics card settings to improve performance.Fast Depth Calculation (may cause flickering textures, try on and off).OpenMP Texture Decoder (in rare instances it can 'max out all cores' and hurt more than it helps).Disable Destination Alpha (may crash, try and on and off).Cache Display List (may crash, try and on and off).Set CPU Emulator Engine to JIT or JITL (if latter may has issues, use JIT.Config -> Enhancements -> Enable Scaled EFB Copy (may be unnecessary).
The latest stable build of Dolphin (64-bit if you have a 64-bit machine) The main fork of Dolphin isn't optimized for running Super Mario Galaxy 2.
