Meezer-Muir

Areas of Improvement: It's called a Wallpaper, not a poster, and the lighting's too dark. Maybe you should change the Night Color in the Background tab of the Project Settings Panel. The monster spawner looks likes it's just a cage. Add a tiny silverfish inside it. Also, add flame particles, and some lighting to make it look more like a Silverfish Spawner, instead of just decorative uses.

good job! Now I recommend setting the flame particle's brightness to 100%, so it looks like fire, and glows in the dark.

Welp...
Due to the realism shader being enabled, the spawner's lighting sucks. I'll have to figure out a way around it.
Fixed it. I'll be adding the new picture shortly.
Done!

I call it a poster because I never actually make it to be a wallpaper. Remember, this is the Wallpaper & Art forum, not just the Wallpaper forum.
I was thinking about improving the monster spawner, but I figured it would take too much time to add the Silverfish. I'll do that, thanks for the suggestion!

I made my first Minecraft poster yesterday. It actually looks pretty good. Whaddya think, people?
https://imgur.com/a/naoyjvc
Improvements
Added Silverfish and effects into spawner, as suggested by MasterArcher12