Attach the grab to the bite. This thing picks up it's prey and tosses it around and then rips it apart with it's mouth. It has claws but aren't used much as it's primary attack. T-Rex with Wings.
Switching the Improved Grab to bite works for me too, at least we seem to have a broad agreement on that.
Shall we start on skills & feats while we're voting on the venom?
Wyverns have the following skills:
Skills: Hide +7, Listen +13, Move Silently +11, Spot +16
+3 racial bonus on Spot checks
Pseudodragons have:
Skills: Diplomacy +2, Hide +20*, Listen +9, Search +6, Sense Motive +7, Spot +9, Survival +1 (+3 following tracks)
+4 racial bonus on Hide checks, improves to +8 inn forests or overgrown areas.
Diplomacy, Search and Sense Motive seem inappropriate, which leaves:
Skills: Hide +?, Listen +?, Move Silently +?, Spot +?, Survival?
Give it +3 racial to Spot like a Wyvern and the pseudodragons +4/+8 racial to Hide?
It will only have 16 skill points (5HD+3 times 6 + -4 Int penalty = 8 times 2) so we'll need to spend them carefully. Might drop the Survival skill if we decide it can't spare the skill points. May have to add some more racial bonuses if we decide to bump up the skills.
I think the bloodstinger is a pursuit predator, so it finds its prey and chase it rather than lies in ambush or sneaks up on it. So, I'd put most of its points in Spot and Survival and a point or two in the others.
Hide 2, Listen 2, Move Silently 2, Spot 5, Survival 5
Add in the ability modifiers and the previously suggested racial bonuses and we get:
Skills: Hide +7*, Listen +5, Move Silently +3, Spot +11, Survival +6
Maybe move a couple of the skill points in Survival over to Move Silently, if we decide it needs more of a sneakiness to tracking balance.
Skills: Hide +7*, Listen +5, Move Silently +5, Spot +11, Survival +4
Hmm, the Move Silently may be a bit low if we go the sneaky route. If we want to mend that we could switch all its survival skill points into MS or give it a +3 racial bonus to Move Silently to get:
Skills: Hide +7*, Listen +5, Move Silently +8, Spot +11, Survival +1 or +4
As for feats, I'd say Alertness (as both wyverns and pseudodragon's have it), plus Ability Focus (poison) from the wyvern, the wyvern's other feat, FLyby attack, is inappropriate as the bloodstinger is a clumsy flier.
Feats: Ability Focus (poison), Alertness, Multiattack (B)
Which do you lot prefer?