1. dynamic water shader
2. particles
3. pcf shadows

• turning them off for animals
• perhaps simplifying them for background or using some kind of pre-calculation.
• There is also the option of randomized jitter / rotating sample window to get a softer shadow with less performance hit.

you need to prerender water normals texture for a set of time, so it will loop or even use some fancy perlin noise texture for that.

Ah yes! Good thinking, :D The simplest solution to pre-render some frames. I actually did this as the first version, long ago but had forgotten!

i dont get pcf

PCF is just basic shadow mapping but taking multiple samples:
http://fabiensanglard.net/shadowmappingPCF/

you should draw into 3 diffrent framebuffers
yes depth needs to be written to texture so you have 2 passes for each framebuffer
one colorbuffer, one depthbuffer
you use same dimensions for all framebuffers, along with same view and projection matrix

It kind of works like this already, a little more complex though as it has a wrapping tiling background bigger than the screen, and handles ground textures separately.

you draw all shadowcasting characters first (in your example it could be trees then animals) to depthbuffer (but no depthbuffer itself but a shader depthbuffer - the one that draws depthtexture) (from light view)
then you draw terrain to depthbuffer and apply lightmap test of depththing we wrote to tex before (from light view :P)
you could even draw a translucent quad in a water place to apply a straight shadow on water surface....

such shadows will reduce framerate by 50% or more

This is how it does things already with the shadows, except I am not casting from the animals at this stage as I figured that would be too expensive, I'll probably just add simple blob shadows for the animals. Although the shadows are received by the animals, from trees etc. The shadow map only needs to be regenerated as you move across the map, it is not rendered every frame.

With the dynamic shadows received on the animals turned off, the shadows on the terrain are essentially free for most frames, but they do cost when scrolling to a new tile.

I have this afternoon implemented the static water as part of the background (although not yet done the bit to add blue colour to under water animals). It doesn't look really bad on my low end phone and is now rendering mostly 60fps. There are occasional dropped frames during scrolling to new tiles but I'll see if I can address that.

I will see if I can add random jitter to the terrain shadows to make it look better with fewer samples.

On low end devices, overdraw and shader instructions are the bigger problems.

Yes definitely, I've been finding this. Has made me so glad I went with pre-rendering the scrolling background as rendering all those sprites every frame would have killed performance. Most of the work on a frame is done by just drawing one big screen size quad for the background. The 'big work' is done when rendering a new row or column of the background, which only happens every few frames, and is limited to a small viewport so it minimizes the fillrate requirements.

See here:

i doubt turning off depth testing for particles will matter.

As well as hardware depth testing (so the particles interact with the animals), the particles and models also can do a depth check against the custom encoded RGBA depth texture for the background, so they go behind trees etc. This is an extra texture read and calculations in the fragment shader so did give a speedup when turned off.

try single sample shadows instead of multiple samples.

Yup I definitely found this to be the case.