A mansalauan is x feet long and weighs x pounds. (We've got flexibility here, as all we have to go on is "Size: S").
Looking at the original text again...
Its main attack is with its sharp tongue, which it can shoot forth from its mouth with great speed. It normally attacks in the same manner as a stirge, seizing a victim in its hands and claws and piercing the neck or abdomen with its tongue. A separate attack roll is needed for the tongue, but this is made at +4 if the claw attack has been successful.
If we add damage to the blood drain/attach, maybe we should give it a separate tongue attack as well? Then we can just say it automatically hits with its tongue when attached and then continues to use blood drain. 1d4 damage?
How about if the tongue has greater reach. If it hits with the tongue, attach kicks in. We could then adapt the following from the mind flayer...
If a mind flayer begins its turn with at least one tentacle attached, it can try to attach its remaining tentacles with a single grapple check. The opponent can escape with a single successful grapple check or Escape Artist check, but the mind flayer gets a +2 circumstance bonus for every tentacle that was attached at the beginning of the opponent's turn.
...for the talons and even tiny arms to grab on.
Here's an attempt at the ability to smell blood...
Bloodscent (Ex): A mansalaun can detect fresh blood at ranges of up to a mile by sampling the air with its sensitive tongue. It can detect wounded, living creatures (except those that do not bleed, such as elementals) as if it possessed the scent ability.