Rather than walking with their body lifted off the ground like insects and for the most part lizards do, yths' proportions make me think of them using their arms to simply pull their body forward over the ground. Throw arms of one side forward, claws pressing into surface, pull body forward across the ground with those arms, throw arms of the other side forward, pull the body forwards, repeat. They could move quite quickly like that, too, I imagine. 

It would rather risk facing ... whatever's down there than hope to get loose before Aemoten can hit it again (I figure the room would otherwise look like a decent lot of hiding places with all the beds and tables and relative darkness)? Okay, so it draws to the right and then immediately starts backing towards the stairs and dragging the guard with it... In which case, Aemoten would still continue closing in, but instead of swinging at it, would actually try to stab/ram into it over the guard's shoulder (sharp edge of sword turned upwards, blunt towards the shoulder of the guard), try to cut off the second stuck arm off too if it seems the guard might fall down the stairs along with it (it should be easy enough to reach the arm seeing where it is anchored, and get the blade under it ... the weight of the guard/yth would actually help to sever it, while the yth would have harder time reaching up because it would be essentially hanging by that point). 

Hmm... Might refine my post a bit after the detailing is done.