The first monster I looked at (Fey Spirit): An at-will area affect power that restrains is too powerful, imo. It'd be much more palatable as a rechargable power.
Yes the Fey Spirit is quite annoying, I can see what you mean about its Psychic Lock power it is very strong against melee.
One of my design philosophies is to create monsters that require different approaches to destroy. The Fey Spirit is a creature that has a powerful area of control up to about 5 squares, but is slow moving. Ranged powers will be consistantly more effective than attempts to melee the creature so a group facing them should adapt their tactics accordingly.
Also while it has some strong control effects its damage is on the low side which reduces its threat level somewhat.
Also Restrained is not really that much more danagerous than immobilised, it has the added effect of giving the target a -2 to attack, making them grant combat advantage and prevents them from being push,pulled or slid.
Having said all that you could change Psychic Lock to a recharge power, if you did this I would recommend upgrading the damage to either 2d6+4 or 2d8+4. The problem with the creature then would be that its only at will would be pittifully weak and the creature would not have as much character. (I know, a highly subjective term)
I hope you do another one of these soon, Mesh Hong. I want to see a compilation of your Slime Beetle/Digester Beetles, and those aberrations you posted over in the Undead thread, in addition to anything else you've made.
I have started work on my next project; "The Book of Distant Stars" which will contain heroic level aberations. Though it could be a while until I have it ready for release.
Anyway thanks for the feedback, I will have a bit more of a think about the Fey Spirit and see if I can come up with a better design.