Archer, the Grell can fly. This one flies at a speed of 60' (with Perfect maneuverability.) As for your assessment that an 11th level party would kick its ass,
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Wow, you are really funny. That's the best joke I've read on an internet message board in a long time. 'C'mon, this thing has AC 50, DR 35/+8, and really high SR! Those poor 11th level characters won't be able to hit it at all, much less do damage to it! As for grappling, even if Close-Quarters Fighting does allow for AoO on creatures with improved grab, it won't really make a difference. The Pseudogrell has a really ridiculous bonus to grapple checks, helped tremendously by its size, strength, and racial bonus to grapple. A 20th level party I could believe. An 11th level party, not a chance in hell.