I know the bite initiates a free grapple attempt, but for the claws to initiate a grapple attempt do both claws have to hit, or only one claw?
If grab is listed next to an attack mode, any hit using that mode of attack will initiate a grapple.
To directly answer your question: only one claw is required to hit. Any time both are required for a special attack to work it is specifically mentioned, i.e. rend.
So if both the bite and claw attacks have the "grab" ability and the tiger pounces, will you get 1 grapple attempt per hit or just one on the first hit?
It works just as if each attack had poison or any other special attack form. Each successful hit with an attack with a special attack form listed can utilize the special attack.
One per attempt until a success, once already grappling grab does nothing for you.
Note that the Grab ability gives you a free grapple check to initiate a grapple, so additional hits after successfully grappling provide no benefit. (but if you hit 3 times, you have 3 attempts.
Fear the zombie pounce tiger.
I just wanted to say that Dire Corbies are the fricking bomb!!!!
Tigers can't finish their full attack action after successfully initiating a grapple.