The 3d instance trails can be done in more than 1 way in Animation Nodes.
First, please note that the example video is actually using 2d footage with alpha (green screen) and basically stacks the img/frames on top of each other. The impression of 3d is just like those Dragon paintings that are allover the net. There is some 3d as the water or such, but that is not the essence of it
To do this with 3d objects, in Animation Nodes I detail in the video 2 cases:
- a very simple motion/transform. this is very easy, just need to read the values for every frame, given a keyframed motion.
- a more complex animation with armature/bones. here there are several solutions, but I prefer using Actions/ NLA strips cause they leave the most computation to Blender and not to python (way slower). just instancing and tweaking a limit to those nla strips
it also includes variants for all frames / offset frames and some indication for further using cycles or scaling effects etc.
AN Motion instance trails 1:
For the 2d effect, you need to stamp the images on top of each other. That can be most efficiently done in Blender using Dynamic Paint, and just stamp the frames with an obj on another. The settings are not quite easy, as you may not want blur or antialias or so, but that is another topic, another q.
Even for your own 3d rendering that should just work, maybe with some extra 3d eff on top, in editing..