Programs:
Blender (v2.79b+) [optional, but 3d models are the easiest way to make something consistent from all angles]
7zip [used to open ztd files]
Image editor with layers and transparency [paint.net is what I'm using]
Text editor [Notepad is fine, but you can also use Notepad++ for example]
APE [ZTStudio (click code, then download zip) is better for animals and allows for larger images, but I still use APE]
Resources:
Snapshots [making of the Ocean Flish model]