What happens if a stirge flies 15ft at a target and fails to "attach" (special grapple initiation)? Does it plummet to the ground and then take falling damage?
Well, yes, in theory if it can't land it begins to fall. Since its probably between 2 and 6 feet from the ground at the time, this causes it no particular discomfort. It is now resting in a square near the PC.
I've never really worried about this. I always describe this sort of thing as batting the creature off with your shield or the stirge bouncing off your armor or some similar descriptive element.
If you did have a problem with this, increasing the Striges manueverability class to the point that it can easily hover would solve the problem.
If it manages to attach, and someone else tries to attack it, what happens if that attacker misses? Is there a chance it will hit the stirge's victim?
Under the rules as written, no. Nor under the rules as written does it matter what weapon you use.
Does anyone else use this creature, or find it a headache??
Stirges have been one of my favorite monsters since the 1e era. I like them because they scale well and are creepy. They show up either as Stirges or as Giant Mosquitoes (with the same stats) depending on my mood and the setting. I'm also fond of templated Stirges - for example I gave a group of them an air template one time and its attack was described as sticking itself down the mouth of its victim and sucking the victims life/breath out of its body.
That said, this is so much more realistic under my house rules if you have rules for clinching and fumbles.
Briefly, the Stirge doesn't 'grapple' it's opponent - it 'clinches'. Clinching is a related manuever to grappling but describes a different situation - hanging on rather than attempting to control the body of the foe. Clinching favors small creatures rather than larger ones, so no special absurd grappling bonus is needed. As written, the Stirge can pin creatures of much larger size and move grapples (essentially drag targets around) despite being much smaller than its foes. Multiple stirges can easily assist a grapple to render larger foes immobilized. This is bizarre unless the stirge is extremely strong! By using Clinching and Grappling rules in combination, you have much more graphic and sensible resolution of small creatures landing on the body of a larger one. For example, under Clinching, it becomes immediately pretty obvious why you would choose to attack a creature hugging your body with your dagger rather than your two-handed sword.
Secondly, I have fumble rules and attacking a creature in the same space as an ally (or yourself) increases your fumble threat range, with any additional chance of fumble resulting in accidentally attacking your ally (or yourself).
