Nice creature, I like it. Also great input from DanmarLOK.
The only potential problems I see with this creature is that it can really only attack one PC a turn, also I can't see a
built in way for it to use Cunning Pounce but I assume you are going to try and build something in to the environment to assist that.
example additional powers:
Blinding Swipe (minor, recharge


)
Attack +11 vs. Reflex; 1d6+5 damage; on hit the target is blinded (save
ends)
Sickening Exhilation (standard, recharge


)
poison
Close blast 5; attack +11 vs. Fortitude; 2d8+5 poison damage; on hit
target is infected with
Strigha's Sickness
Strafing Strikes (standard, recharge


)
Strigha makes a Claw attack against a primary target; hit or miss Strigha
may shift 3 squares and make a Claw attack against a secondary target;
hit or miss Strigha may shift 3 squares and make a Claw attack against a
tertiary target; if this final attack hits it may also make a Bite attack
against the tertiary target
Retreat into Shadow (immediate reaction, encounter)
when hit by any
attack
Strigha becomes invisible and shifts 6 squares as an immediate reaction;
this invisibility ends in Strigha is hit by an attack or makes an attack
What's Strigha's Sickness and an infliction that's automatic on a hit from an at-will? You'll have the whole party down with it over the course of the fight.
Yep, it's a disease. Wererats have at-will bite which inflicts filth fever. Do you think it's too much for a solo to have? I mean, it is dependent on another attack hitting first. Also, the PCs will have advance warning, visiting with a comatose victim of the strigha's previous attacks.
I wouldn't worry about the disease, in my experience PCs will shift the disease very quickly. Cure Disease is only a level 6 ritual and makes even level diseases trivial, if you want a disease to be an actual threat you have to make it a lot higher level than the characters (which never really seems fair to me).