Why would you wait till level 16? You can get it at level 7...
Here, do something like this. No flaws.
Lesser Aasimar Bard 5/Unseen Seer 2 (at this point you have hunter's eye)/Lyric Thaumaturge 3/Sublime Chord 2/Hathran 5/Incantatrix 3
Feats:
1 - Ethran
3 - Melodic Casting
6 - Leadership
9 - Extend Spell
12 - Persist Spell
15,18 - Free
Circle Magic yourself up to high CL, then persist Hunter's Eye & Shapechange. Change into a Gloom. You now have sneak attack +26d6.
You have Hunter's Eye at 8th level (for +3d6, which becomes +4d6 at 9th), and polymorph at 10th level. Nice scaling, very powerful. With flaws, you can pick up Dragontouched and DFI at 1st level, you can get Song of the Heart at some level, etc.