Made a quick Mind Flayer class, went with wizard HD and skill numbers. It is up for discussion and moving stuff around naturally but as you can see stacking this with another class will make a rather formidable character. 

I do realize that due to not including HD in the overall CR it means you will get very powerful abilities very fast like plane shift at will at level 8. I do not want to utilize HD as well because HD is even worse of a judge than CR.

Mind Flayer
HD: D4
Skills: Int+2

Levels:
1: +2 INT, +2 Wis. +1 natural Armor, 2 tentacles 1d4, Telepathy 10 ft
2: +2 Cha, +2 Con, Psionics (detect thoughts, levitate) Telepathy 20 ft
3: +2 INT. +2 Dex, Mind Blast 1d4 rounds 1/per day (1 target), Telepathy 40 ft, 
4: +2 WIs, 3 tentacles 1d4, Improved Grab, Psionics (suggestion), Telepathy 50 ft
5: +2 INT. +2 Cha. +1 Natural Armor, Mind Blast 2d4 rounds, 3/per day (10 foot cone), Telepathy 60 ft
6: +2 Dex, +2 Str, psionics (charm monster), Spell Resistance 15, Telepathy 70 ft, 
7: +2 INT, +2 Wis, 4 tentacles 1d4, Mind Blast 3d4 rounds at will (30 foot cone), Telepathy 90 ft
8: +2 Cha. +1 Natural Armor, Extract, Psionics (astral projection, plane shift), Spell Resistance 25, Telepathy 100 ft