I have finished the Moth Wings Shrug, and I love the lacy look and join as you go construction. The sleeves in particular are cleverly constructed. But I will admit it took me several minutes of pondering and tearing out my first attempt to join the first sleeve motif followed by several more minutes of pondering to truly grasp this clever construction.
On the last row of first full motif of the sleeve, you do not join on the first corner. Work the first corner as for the full motif and then work the next 2 ch-3 spaces. Now you will begin joining the working motif to the underarm motif.
The first motif you will be joining to (your adjoining motif) is the unworked motif from the base row. Chain one and slip stitch in the 4th chain-3 space of that underarm motif. This will be the chain space just off of the center of the motif. Continue joining as normal through the chain-5 space and up the first motif vertically up the armhole. Then work the rest of the Round 4 around the working motif. You will notice that only half of the working motif is joined to the underarm motif.
Continue joining the motifs around the armhole to the last motif to be joined. Join this motif vertically to the last vertical motif of the armhole, then continue joining to base/armhole motif. You will only join halfway across this motif (the other half is joined to your first motif). To join the rest of the unworked side of the working motif, begin joining in the unjoined half of the first motif worked for the sleeve.
When you are finished the underarm/base motif will have two different motfs joined to its top, and those two motifs will also be joined to each other.
I hope this help you visualize the join, and let me know if you have any more questions. It has been marvelous crocheting with you. I think I am starting a second shrug for myself. What have you thought of this shrug?