Thanks for all the comments guys!
That frog is just unbelievable.

For larger scales you should try a similar technique but casting it first in a semi-transparent resin whose you use instead of a base layer...
I've seen that done with resin portrait busts and the final effect is stunning. It would suite a subject like the frog very well.
You will be the perfect person to show this off. AFter trying to go light on some dark layers and it not working some time ago, I was thinking "Just use the same technique as is used in watercolour, leaving the white of the paper for highlights". Very tricky in watercolours, very easy in mini painting! Haven't got around to trying it yet myself, so I watch you with baited breath!
dfb
Yes you are spot on it's just like water colour painting! I think it's a quicker technique than traditional shading highlighting but it takes a light touch. You need to progress very carefully to avoid building up too much paint and losing the translucence.
How about some flowing water running underneath that real frog you somehow got to sit still, and have it cascading down the rock face ?
The base does cry out for it doesn't it. So I think that will be a yes to the flowing water!
One thing I would ask is are you going to make the frog look wet, as they have a sheen to them due to the mucus they exude ?
How could I not include mucus! I'm experimenting with some different finishes to get just the right wet sheen. I also want to include some water droplets here and there but that is proving tricky. I'm going to see if I can do something with glass microbeads.
I've made some tests sponging on gloss acrylic varnish to try and give the look of patchy water droplets but it didn't work out. The moment I started to dab on the varnish it went frothy! It dried to a very interesting (and slightly unpleasant) effect that I've mentally stored away for later use.