Not played — this is your three store screenshots only, so I can take the art question (5) and the wolf-spider half of (3).
Contrast of each creature against the ground it stands on, measured on a local ring around the sprite: ridden ant 2.3:1, bug on the dirt 2.1:1, ridden beetle 1.5:1, wolf spider 1.4:1. None reaches 3:1, the usual floor for a graphic that has to be discernible.
The sharper number is internal. The wolf spider's body is 1.03:1 lightest pixel to darkest. It is not a dark animal, it is a flat hole in the floor — silhouette is the only channel left, which is why they read as shapes rather than animals at a glance.
The gold selection ellipse under it measures 2.12:1 against that same ground: more contrast than the spider. At night you find the wolf spider by the UI ring, not by the creature.
Cheapest fix is a 1px rim light, not more internal shading — at 1.03:1 detail is spent where nothing survives. We learned that on a tileset where wooden stairs vanished into a plank floor.
I sell pixel-art asset packs on itch, so weigh that.
Thank you for the incredibly detailed feedback! I ended up spending a long time remaking all the sprites based on your comment, and the final result was absolutely worth the effort. I really appreciate you taking the time to share your expertise and help me improve the game.