>>2115859
A dev diary is usually a long-form blog post with a detailed overview of the plans for a tag. Kaiserreich's dev diaries are a good example of what people usually expect. The format can vary, but usually it's a lot of text with screenshots to accompany it.
A teaser/toozer is usually just a stylized image, showing off something like a focus tree. It's more meant to capture someone's attention, while a long-form dev diary is better for explaining things to your existing fans.
Picrel is a toozer. It's eye-catching, but doesn't tell you much. A dev diary would instead have something like several paragraphs abouot what the actual unification war might look like and what the backstory for this tag might be.