I want render meshes like the way render the stingrays/whales like this video Is this all particle effect or a mesh / shader effect with some particles thrown in? Is there any assets / or shaders or examples that get closed to this? Thanks.
You would use meshes and particle systems, but the meshes would mainly be to drive some particle targets. Keijiro has a lot of useful resources to put stuff like this together https://github.com/keijiro/Smrvfx https://github.com/keijiro/VectorFieldExamples And a bunch more VFX examples on his profile.
Visual Effect Graph would also save a lot of time with this kind of effect, but you need to construct some tool or use existing ones to get animated meshes in. All those blinking and deformation effects would be then quite easy to do in VFX Graph.