How about DR 10/lawful? DR /magic is so weak, especially once characters are traveling the planes.
The bite of a tener is venomous and causes paralysis for 6-36 turns (save at -2).
Rather than making its bite inject poison, how about just modifying the carrion crawler's paralysis ability?
Paralysis (Ex): Those hit by a carrion crawler's tentacle attack must succeed on a DC 13 Fortitude save or be paralyzed for 2d4 rounds. The save DC is Constitution-based.
6-36 turns equates to 1 to 6 hours!
The save at -2 implies Ability Focus or a racial bonus to the save DC.
For the improved grab/maul, which approach do you prefer?
Improved Grab (Ex): To use this ability, a tener must hit an opponent of any size with a claw attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it wins the grapple check, it establishes a hold and can maul.
Maul (Ex): A tener grappling an opponent with two or more of its claws deals automatic bite damage each round it maintains the grapple.
-OR-
Maul (Ex): A tener that hits an opponent with two or more of its claw attacks immediately hits with its subsequent bite attack.
This is how we did it with the mara...no improved grab at all. More like rend. We can still give it improved grab, but needn't tie the maul to it.