The yiga hideout is supposed to be closed for that, you have to enter from the rear. As for the rings, maybe you're just not looking in the right place? There's a lady with a bunch of sand seals near where the rings are, so if you haven't seen her then you're not in the right area.
Triple attack boosts are helpful in getting his hp down quickly to get to the next phases. Also, Urbosa’s Fury is useful to stun him in a pinch. It only works once, but when he’s got all those clones out, setting down some mighty bananas will distract him and reveal the real one (which is really...
The third trial was satisfyingly hard, not unbeatable. This isnt nearly that hard, anyway. You just need to be sneaky and good at dodging when necessary.
Ok now that I've beaten it I can say... THAT WAS AMAZING! I loved every minute of it. The One Hit Obliterator trial was artificially difficult, but the shrines were very creative, as were the Champion Trials. The new memories were amazing and everything I was hoping for. I have a new...