I've been working on my Riptide Y'Vahra conversion for a few evenings and this is what I've come up with so far.
I had to create the head from scratch using left over and broken star wars, transformers, and 40k Imperial/Tau/Chaos bits to give it a bit more heft compared to the original. It's a bit too big IMO but I still prefer it to the Thrud the Barbarian tiny head the original model came with. The arm was similarly created and I'm happy with the final effect there. Unfortunately, I wasn't able to successfully magnetize it to allow fast switching of the normal riptide arm with the Y'Vahra variant weapon. I figured I'd probably be playing the "normal" riptide more often and wanted the suit to look like a bigger upsized version of the smaller one so opted to glue that arm on.
One thing I'm definitely not happy about is my scratch built shoulder pad. It just seems both too busy there as well as out of place. I've since taken it off and repositioned it both higher up on the shoulder as well as reversed (so the short face/angle is pointing toward the elbow instead) and it does look better but I'm still not happy with the result. I'll be trying to pick up some armor bits on ebay to test out a few other looks but for now both the shoulders are bare.